Has anybody compared the CPU usage of various output methods (analog vs adaptive USB vs async USB vs S/PDIF)? I don't own any DAC yet, so I can't do the comparison myself. In fact, I'm asking this question precisely because I'm looking to buy a DAC with headphone amp for my MacBook Pro. Of course I want better sound, but it would be bad if I have to sacrifice too much CPU time. I chatted with a sound engineer on IRC and he said he once tried outputting to a DAC via USB and it ate up 40% of the CPU time, so now he prefers FireWire. Unfortunately, I couldn't ask him what kind of USB strategy (adaptive/async/other) and what computer specs he used before he left the chat room.

Don't panic, 4-10% for 44.1-192kHz through USB on a 3 year old MBP.