I don't know any detail about the chip, but if you want anything "special" (analog surround out, etc.) you have to go with a PCI or USb based system, thanks to Apple Corp.
Audio is processed through the CPU. That's why UT2004 gets a boost with dual processor machines. The game isn't multithreaded, but it does use the second processor for sound processing. On a PC this is done on the sound card.