Audio PC

I plugged my computer into outlet on different phase (I use WiFi).  Digital transmission may produce timing jitter that will translate to added noise, proportional to signal and present only when music is present, causing loss of clarity (during gaps it is completely silent).  Should your PC be built for this purpose - it depends.  If you use WiFi then computer doesn't matter (I use it for other tasks while playing music).  Same goes for Ethernet or USB.  Slower computer might be even better polluting less (lower speed, lower power).  With S/Pdif it might be better to dedicate computer to this task only.  You will have to experiment, but people reported better results with faster dedicated computer, free of other tasks.

Regarding inteface - if you're using USB, then you need an ifi isilencer USB dongle. This will correct timing errors between the DAC and your computer.

There is no timing errors between DAC and computer with asynchronous USB.  Computer sends data in "frames", likely at 1kHz rate, while DAC places data into buffer signaling back buffer under/overflow.  Upon this signal computer adjusts size of next frame.  DAC takes data from the buffer and feeds it to D/A converter at different internal clock.  That way data is not missing, in spite of different clocks, and there is no timing errors.  The only possible issue with asynchronous USB is injection of electrical noise from computer by the cable.