if I could rig a PS3/XB360/Wii to a PC - would the amBX work then, or would it have to be a DVD/amBX game?
Probably not. I suppose it depends on what you mean by rigging it to the PC. The only way I can think of is if the PS3 etc. video signal is input to the PC via a suitable video converter, and then I wouldn't guarantee it. I suppose it depends if AMBX detects the video properly. I don't know much about the gaming etc. side, but I assume that however the PS3 was rigged up to the PC, even if the AMBX did work, there would be an increased delay between the action that you're seeing on the screen from the PS3 and the AMBX lights. Even then, any light reactions would, presumably, be based on the screen content, rather than the games' built-in AMBX commands
Somebody else here may have more experience with what you're thinking of possibly doing and may be able to give some advice. Personally, I don't think that you're going to have much luck with connecting anything external like the PS3 etc . and getting it working realistically, so you'll just be able to use the AMBX for whatever you have on the PC.
However, the AMBX is also very good just as an ambient light set up, whether it is reacting to the movies / DVDs etc. played on the PC, or the audio input, or just the lights on their own based on various scenes or settings. This is especially so when using the Aurora Synethesiser programme that you can download to work the lights.
I have a music source where the digital audio output goes to my amplifier and the standard phono output goes to the PC audio in. Although I don't play the audio through the PC, Aurora Synethesiser uses the audio input to control the lights according to what the frequency of the music is. Ii does look very good,