Here's my suggestion:
First, let's address the QSC gear. Now, your subs and tops are all active, right? OK, good. And I bet your subwoofer has a high-pass cross-over that you CHAIN to your top's input? Right? I'm fairly confident I am right. OK, so now, with driver specific amplifiers driving each driver within the units, you have an active driven system that is already OPTIMIZED for peak performance of THAT GEAR.
But are you? That's the biggest question. It's a matter of "just because the gear is optimized to work doesn't mean it truly is optimized".
Now, mind you, your QSC gear, nothing is wrong with it. Don't change your wiring.
But here's your ideal signal path:
Mixer output to RTA or front end processor(typically a real time analyzer). OUT of the RTA to the amplifiers(or inputs on your subs, which are in turn cross-over to be chained to the tops).
Using a decent quality reference microphone, which you can get for a decent price(say, under $200 really, but you can go nuts if you want).
Here's what happens:
The signal passes though the mixer and the RTA. The RTA might also be adding things like limiting, feedback killing, compressiong, delay and EQ. As the signal passes THROUGH the RTA, it is also listening to the reference microphone. Ideally, you should make a CD with reference tones and pink noise. Send pink noise through the mixer and then through the RTA. Let the RTA listen to the pink noise and compare that to what is passing through it. NOW it will hopefully opmtmize your EQ for the room. NOW you are truly optimized. You want the room as flat as possible. By "flat", I don't mean dull and lifeless, but rather "theoretically, all frequencies SHOULD be represented equally". Of course, I always then end up bumping the bass by about 3-6db afterwards, but that's just me.
I spend over $50K on my KV2 rig(and I will be buying more) and same on my console. A $1500 RTA is definately a necessity. BUT, I'm not saying you need to spend $1500, but I need a LOT of features. Not to mentiom brands, but for around $400(and you can do better), Behringer makes a budget conscious RTA(and spend an additional street $90 for their mic). Sure, ain't as full featured as my Sabine, but hey, it will get the job done quite well and it sounds OK.
The difference an RTA can make can quite literally be that "without being used, your banging gear can sound like ass" or "with an RTA, you can ensure coherent sound with minimal distortion and thus reducing ear fatigue and increasing audience enjoyment". As I've said, great gear gets you a long way, but not all the way. At some point, skill enters the picture(but to a far lesser degree for DJs). It takes less skill to playback pre-recorded music than to deal with live musicians. And using this RTA isn't a one-off "set and forget", it's something you MUST integrate into your process and repeat in every new room(or every gig). My RTA lets me save stuff, but I never do. Would save time, but I don't to too many repeat venues, but that appears to be changing.
Now, back to pracicing. Yeah, I know what you mean. Working with my Mackie 1604 VLZ, it's easiy, I know what's going on at all times. With my ProMix01, I had some issues, UNTIL I did something about it. And really, I could have had this issue with the Mackie 1604 as well, but the layouts are vastly different and with the Mackie, it has features I needed that the ProMix01 does differently.
The Mackie console is designed for "all purpose usage", where in my opinion, the ProMix01 is more of a live console or a small mix-down/monitoring(not MONITORS) console. So, I got the chance to hook the ProMix01 up to, in my case, a small set of mains(my larger near fields) off the main outs , , another small set of near fields(My KRK 6000's) off the MONITOR outputs, and a set of headphones to the headphone outs.. NOW I could fully explore how Yamaha's line of thought worked.
In my case, this was easy. I've got tons of gear laying around NOT always being utilized. I sometimes need to remind myself I have this stuff. And you'll note I often think outside the box.
Take this next part with a grain of salt. Personally, I'd NEVER run a DJ console right to the mains. Here's the first reason why you need to take this with a grain of salt: Most DJ's have no concept of gain structure. RED is not a good thing, so I typically have to run them into channels on my console and then insert a limiter to prevent them from blowing things up. Of course, your QSC gear, like my Mackie SRM650's and SRS15500A's, as well as my KV2 AUdio stuff(and my other QSC amps with community speakers) all have limiters to prevent overload and damage, I'd prefer to NOT have the limiting happen at the amplification layer, which puts things dangerously close to clipping, which is where the real damage takes place anyways. However, the concept of those limiters is to PREVENT clipping to prevent damage. Still, running in the red is bad. Peaking in the read is OK, but living there is NOT acceptable. The second thing is that I just prefer to have another layer of control, but that's just me. I mean, I'm dealing with up to 76 channels of input and making a cohesive and coherent mix of a live band performing, which is vastly different than a DJ environment. Still, it's something I recommend. So, take that how you want. If you're running a microphone, you should have a mixer with an insert on the microphone channels so you can at least stuff a feedback killer in there if necessary(on the insert loop). Mix your vocal/MC/talk mic into the pre-recorded mix.
Do you have to spend $50K on a mixer? No.
For example, you're learning. That's well established. The next step is "well, crap, I really have to understand what is going to mains and what is going to my monitor/cue mix" as well as "and I don't want to waste money doing this as well as wake the neighbors". And how do you do this? Why, with a second mixer, of course! You take your MAIN outs from that DJ mixer into another mixer that would NORMALLY feed the mains or RTA-mains. For a budget, you could go with a dinky little Behringer Eurorack UB502, which is a tiny little super basic 5-channel mixer(1 mic, 2 stereo inputs, as well as tape/rec loop). Super basic, should cost you less than $50, but no phantom power on the mic, but you probably won't need it at this level. But keep in mind, my objective here is to help you practice for cheap, not necessarily make better recommendations for your actual events. While I have 2 of these dinky mixers, I also have the 602 mixer, but neither of which I'd use for my main signals to pass through. I typically use them at home for some monitoring purposes or on stages for the similar applications.
Want to get more advanced? Get 2 sets of headphones. But if it was me, I wouldn't. Just plug/unplug as necessary. So, if you're unsure what's going out to mains, move your phones around. Anything plugged into the "mains emulation" is what is going OUT through your mixer to mains. Now you can learn your cue system with confidence.
Another option is to go through your home stereo as your "mains" and turn the speakers off and use the headphone OUT on that. What's good is this is a better "emulation". You may need adaptor cables, which can be had relatively inexpensively, and you might be able to leave in place for practice lateron. As I don't know the interface on the unit you're talking about(the American Audio unit), I can't advise further other than you can talk a balanced signal and not transformer match it if you short pin 3 to ground on an XLR or balanced and then take ground and pin2 to HOT for your unbalanced and it should give you a -10 connection. If you short pin 2 instead, for some reason, that gives you a +4 unbalanced signal. I could be wrong about that.
I know, talking about taking a while to get there. I like to be verbose, but for a reason.
Now, go screw up some more!
I used up a LOT of gear to learn my ProMix01 because it was necessary for me to totally grasp how Yamaha did things. I did NOT need to do this on my Mackie 1604, and not on my A&H ML5000 48B. I take whatever steps are necessary to educate myself on my gear, including trial by error. Typically, nobody books me in January(2009 is different), and I spend that month re-certifying every bit of gear, wire, connector, you name it. That's also maintenance and education cycles. But now, I have so much gear, I only really need to learn the new stuff. An FX unit, some outboard, wireless stuff, testing wiring, things of that nature. But realize we're at two totally different levels.
So, I say "go screw up some more and have fun doing it".
Oh, further advise: I would recommend a set of closed back headphones by Ultrasone. Good sounding and good isolation. My KRK240's absolutely rule in the studio, but SUCK when I take them out live. The semi-open design gets lost. I've switched to using a set of wireless in-ears for the time being for my cue/AFL/PFL/SOlo monitoring applications at FOH.
Hit my web site up. Hopefully it's working. Don't drool on the keyboard too much!