Unless you want your program to alter/process music (like upsampling) playback program should not matter with asynchronous USB since there is no timing in this scheme (data sent in packets).
Computer noise is always important since it affect DAC's noise. USB cable should have only data wires - power should not be delivered to DAC from the computer.
Computer noise is always important since it affect DAC's noise. USB cable should have only data wires - power should not be delivered to DAC from the computer.