XMA certainly — every game uses it, and it's the primary audio format for the Xbox 360. It lets you store between eight and 10 times as much audio into memory. That makes a HUGE difference what a sound designer can deliver. I also found Halo 3's use of the Waves technologies very cool, and we're excited to have partnered with them. Actually, one of the "most interesting features" that has been used is just the fact that, aside from XMA, we've moved to an easily programmable software audio architecture. I've seen some games do some amazing things because they could just write some C code, either for DSP effects, 3D or entire audio engines. It really has unleashed a lot of creativity in my opinion.

Some obvious advantages are pooled memory and the cell architecture that allow for some serious processing power for more real-time interactive mixing. More channels are good but not necessarily always better.