Are you running the digital signal through the same DAC as the rest of your system? Does the M-audio card process that digital signal in any way? I suppose jitter could be a potential problem. Regarding alternatives: It depends on how much you are willing to spend. I'm not sure how you are running the digital, and through what processor(s). I would certainly not use the analog outputs of the M-Audio card and expect it to be the equivelant of a good DAC. You could try one of the USB dedicated DACs such as the Apogee that take the digital signal from your USB port and forget about the card altogether. I believe there are some very expensive DACs that have a Firewire option as well (Elgar). You may also want to go over to PC AudioAsylum to get more input than you could shake a stick at on this and other PC Audio related subjects. On my secondary system I've been running an AirportExpress through my Mac going digital (toslink) out to my DAC and it sounds great to my ears. I cannot hear any significant differences between the transport and the computer clicking back and forth that would make me want to give up the convenience of the hard-drive library (of course they are going through two different inputs on the DAC so not really a fair comparison). Regardless, the sound does not leave me wanting to improve upon it.
Marco
Marco