I'm new in computer-based music, and I'm pretty confused and happened to have the similar question. I would very appreciate if someone can offer the guidance:
1) If my lostless music is only converted from audio CD (16 bits/44.1Khz), would that make any difference among USB, TosLink or coaxial output to my DAC? If my DAC has upsampling, like MF M1 DAC, would that make any difference for the question?
2) If even there is no difference among the differenct output interfaces, considering the max sampling limitation for 16/44.1 source, is there still some possible sound quality difference? I was told that USB communication may be easily affected by unstable computer power supply, and that may affect the sound quality. Does that mean the digital data will not be "lostless" over the USB communication between computer and DAC? How is the situation if we use coaxial or "Mac->AirportExpress->Toslink->DAC"?
3) The other question is about the Software for the music source. I saw some people posted that Foobar may have better sound quality than iTune as the music source. Is it true? If I got the same lostless music file, shouldn't that be the same no matter I use Foobar or iTune to play and send the music bit streams to DAC via USB or coaxial?
Any comments will be very appreciated. Thanks.