Well, you're stepping into a situation where you have too many choices.
First, I strongly suggest you don't run your recording and your DJ/mixing performance on the same machine, and ESPECIALLY not over USB(it's half duplex, you'll be choking it via the same I/O). I had a guy struggle through this recently and he just wouldn't listen, and finally he gave up. It's mainly an I/O and CPU overhead issue. The DJ software can be quite demanding, as well as the needs of the recording software.
There are multiple ways to go about this. It really depends on what you want to do and how much you want to spend.
First, you want to put quality first, which excuse me for getting up on a soapbox, but if you're using MP3, you're already taken your quality and flushed it down the toilet. Stick wiht CD-quality 16bit/44.1K files, OK? Otherwise, it won't matter, it's gonna suck, just harder.
Now, we have to look at how you're working. I take it you are muxing via the AA MX1400 mixer, so that's your main platform, and then your Mac laptop is your recording source? Is this true? Or is the Mac also audio source? You mention Tractor and Virtual DJ, so that kind of throws things askew until you answer better.
Recording interfaces can be had for anywhere from $99 to, well, let's just say they can get rather expensive. The good entry level interfaces hover in the $200 to $250 range. Small jumps add small improvements(more ins/outs, better pre-amps, maybe a goodie or two). Then on top of that you need your recording software, which can vary depending on your needs and the interface ProTools M=Powered will run you $250, while Pro Tools LE, I forget, but it's more. But, that's not to say some lower-end products aren't worth checking into. There's some free stuff, but I never recommend that route. Sonar Home Studio runs around $99 and really, it's not too bad for basic work. Some of the hardware may come with software. Don't waste your money on ProTools unless you're buying ProTools hardware, but you can use third-party software with ProTools hardware. In most cases, we're doing a analog to digital conversion.
Doing a digital to digital, you need to pay closer attention to clokcing, so you want to set thing to 44.1, which rules out regular off the shelf DVD burners(if they have digital input), because they lock up at 48/96 for input. If you're not clocking the same, it won't work, so just be warned.
Other options include stand-alone CD burners, MiniDisc, DAT(rare, don't waste time on it these days), digital tape, and even pocket-sized digital recorders.There's also way more options than that. This is justt the tip of the iceberg.
But perhaps you don't need much at all. I mean, if you're using disc-based files on your MacBook, why even bother with all the rest of the stuff? Unless you're scratching or using FX on the DJ mixer or other performance elements, why bother with that? Use the mixer for listening/monitoring, and then simply mix in the box using Sonar, for example. I mean, I love ProTools hardware and software, and it's typically the best route, but in your case, if there's no valid need, then why bother?
There's lost of questions still needing answers:
Are you planning to do this live? Do you want to mix in some house mics for ambience?(might be cool but ups your costs), or is this ia studio/controlled environment? What's your budget? How many main outs do you have? I know I could get some of these answers by RTFM for the AA MX1400 mixer, but I ain't gonna.
So, start thinking methods, post production, editing requirements, length and purpose.
