I'm using iTunes to keep track of music ripped in Apple Lossless on an external hard drive on my Powerbook G4. I use a Scott Nixon USB Tube DAC (USBTD)and 15' USB connector. Previously, I used an Apple Airport/Musical Fidelity Trivista DAC 21, but I think the Airport created too much jitter and I couldn't hear the full benefit of the DAC 21. The Scott Nixon sounds much better. Soundstage is bigger. Bass is more defined. The sound is less fatiguing, even with 128k MP3's and internet radio. I'm sold on USB DAC's.
Mark
Mark