This has been an area discussed MANY MANY times on the forum. But here's a summary:
Not all lights that support a sound active stand-alone(or even master/slave) support sound active when in DMX mode, so PLEASE PLEASE do read your manual in regards to any and all fixtures you own that have DMX functionality.
In my case, I know for sure my ADJ 64 LED Pros, Mega Panels and Mega Bar 50's all have a sound active capability when in DMX mode.
Now, getting back to DMX control, and let's say you're using MyDMX:
You can make a scene that is "wash scene", where you turn ON what you want, then the announcements are over and it's time to get the show rolling again, you can click another button to get to your "sound active" scene, should you program it correctly.
Similarly, you can do the same thing with a DMX Operator, you just have to pay closer attention to what bank you're on and what bank and what scene within the bank does what so you might want to have these documented.
In a real world example:
In a show I do, to save programming headaches, during one section, I just chuck my 64 LED Pros and Mega Panels into sound active mode(along with a few other lights), while the Mega Bar 50's stay pink to wash the stage with some steady light. After a certain point, the scene changes do a solid color and all the LED's go to that color(while another set of lights goes off). It's really as simple as that.
So, in summary, read your manual and DMX traits to see if sound active is supported in DMX mode. If sound active is a "drop dead" feature for you, and it sounds like it is, double check any fixture before you buy it to make sure it has a sound active mode in DMX, then you should be fine.
There's also a primer on DMX here on the Elation site.
DMX 101 HandbookI would read this and get familiar with DMX in general terms. This won't answer ALL your questions, but it gets you started. For product specific questions, you have to read those manuals.
For controllers and software, it's best to probably ask questions for now, while reading the manual. The manual for MyDMX may be an overload, while the manual for the DMX Operator might not be super helpful, and the section in regards to programming is a little unclear if you're not in front of the unit while reading it.