Sounds fun.
In regards to sound response: Right. MyDMX does not accept sound response input. You could use some sort of sound/trigger to MIDI controller to trigger scenes. Something like a drum brain comes to mind but probably won't have the type of control you want.
Backup option? Having a hardware controller laying nearby for back-up is a good back-up. Maybe a second laptop hot and ready to go? Swing the USB cable and away you go? If you go with a controller solution, swing the DMX cable over and your downtime should be minimized. The controller may give you the audio response you are looking for. Keep in mind the audio response happens via the little dinky mic IN the controller.
Will lights be killed? That depends. For example, my Par64B LED Pros will stay on the last scene for a few minutes when DMX signal is lost. Most of my other DMX fixtures simply turn off. My dimmer packs go wonky while in DMX mode when they lose DMX signal. So that issue is really more fixture dependent.
Any way to daisy chain? Not really a smart thing to do with asyncronous signals, especially those that work in a serial-type environment. Dumb move, guaranteed to be a problem.
While MyDMX mimics a board/controller, it also can handle programming of more complex things that a SIMPLE console can't do, but maybe some mid to higher end units can handle, which makes MyDMX really a cost effective unit.
I think you can do what you want with MyDMX. Make a LONG SHOW, say maybe a half hour or hour or so, something where you don't need to live at the operator position, but long enough where you can do a check-in and reset it before it ends and needs to be restarted.(the show, NOT the computer or MyDMX).
Now, my take on MyDMX over ShowExpress:
I don't like Chauvet's tech support, when and if you can get it. ADJ support has been wonderful.
In my scenario, I have both MyDMX and a DMX Operator. I could if I needed sound response, run a"zone" that uses sound response off my DMX Operator on a totally independent DMX run, while MyDMX can be on it's own run handling the rest of the environment.
You can also toss lights into sound response only mode(stand alone), or use the DMX value for Sound Response mode, where they will sit in sound response mode until you take them out of it(via DMX control!) Of course, realize via other discussions, that there is NO syncronization of same fixtures in DMX Sound Control mode, which I think would work in your favor for this environment.
Ideally, depending on what you want to do, it may be possible that you don't even need a controller, much less MyDMX.
I can't really made any recommendations which absolute way to go without being directly involved in your vision, and I don't want to be involved. No offense, it's just my plate is full as it is. What I do think is that you've got a good idea that can be nourished and allowed to blossom as you gain experience and learn more. And because of that, you need something that will grow with you. At the same time, is this a one-off thing, or a once a year thing? Or do you intend to get a lot of usage out of this gear?
As a sound production company, I need to be running, period. MyDMX didn't work on my for a big show, so I had my DMX Operator that saved me for that show. Why MyDMX failed is not important, because MyDMX has worked fine at events since then. I don't have time for excuses, the show must go on!
Assuming that MyDMX is rock solid, which it appears to be getting there, and all other things considered, you can go with a entry level type controller like a DMX Operator, or for a bit more, go MyDMX. Why? I think it's money well spent, and not just because I bought it as I technically didn't need it. I can't say I'm disliking my purchase, I'm super pleased. I think the 3D Visualizer will be a very important tool for you to use. Design your environment, place your fixtures, and then do your lighting design. For me, having that sort of tool is super important because it's not practical to set up stuff and see what I'm doing on an actual console. I can go sit on my sofa while my truck is full and a mere 25 feet away(and locked up), and try to design my lighting show.
And again, back to support. ADJ seems to actively supporting their products. I don't see Chauvet showing the same level of interest in their customers.
Not to sit here and be an ADJ fanboy, but I'm pleased with the company. While I do have some Chauvet fixtures that I am pleased with, Chauvet's support to me has been less than satisfactory, trying to more point blame at something I am doing as if "their product is so perfect it sets the standard". If that's true, then I am very scared!
I think Compu Live is a bit much of a jump.
Keep in mind back-hauling MIDI signals for singalling back if you need audio response. I'm sure you could get a sensitive microphone coupled with a compressor/gate/limiter with side-chain to trigger a drum trigger to get a singal response back. You can use MIDI mergers/routers such as an MX-8 that might help you in those regards. This can get as complicated as you want. Bring the mics to a console with phantom power, you can use better microphones, centralize your audio response functions, as well as centralize your outboard. You can run this off your insert loops. Since you're not using the microphones for running audio through the system, you burn channels, but you can reserve a few for your pre-recorded audio feeds.
This can get as complicated as you want. Have fun!