Not sure about the Audigy, but I use a USB Creative Labs Sound Blaster MP3+ (AKA Sound Blaster Digital Music) on my TiBook and get noticeably better sound than Apple's onboard. Creative doesn't make Mac drivers for it, but Panther recognizes it automatically as a generic USB audio device and lets me use all of its inputs and outputs, including optical. I would think (and hope) that if one USB Soundblaster works, the other would work as well.