I have about 160gb of uncompressed CD/AIFF music, and I was NOT impressed with the Transit, terrible drivers, and the output via optical was sub-par compared with my rotel RDV-1060 dvd player. We're not talking about a 'subtle' difference either, my non-audiophile friend who was over with the Transit was like "wow, that really SUCKS in comparison." This was after we spent almost 2 hours getting the stupid thing to output at 44.1/16 since it INSISTED on trying to go to 48khz (sounded even WORSE). From reading a lot on HeadFi and elsewhere, I too recommend the Firewire Audiophile (supposedly better drivers) or look into Edirol (Roland) such as the UA-25. Too bad you don't have a pcmcia / cardbus slot, as I've also heard very good things about the Echo Indigo card.
I'm looking to do the same, with my 15" G4 Powerbook - I may just go with the Echo Indigo - but my only worry is being partially internal to the computer, that it might pick up hard-drive / processor noise. If that's the case I'll try something like the Musical Fidelity X-DAC v3 and find a decent digital out via PCMCIA or external, via FW or USB, similar in function to the Transit, but a Transit will surely NOT be part of the system. I used to use a G5 w/ built-in optical but now I need the portability of the Powerbook, dammit if only Apple put optical on the PB, and it's too bad the Airport Express has mini-1/8" optical as I've yet to see a quality TOSLINK (boy is THAT an oxymoron) cable in that format...
