Knownothing, In asynchronous USB computer downloads
"frames" of data every 1ms into DAC's buffer. DAC sends back
buffer under/overflow signal to reduce or increase size of next frame. That
way no data is lost. Next, DAC takes words from the buffer and loads them
into D/A converter at its own internal clock. This scheme makes computer
irrelevant. Use any external HD, USB or not. It won't make a difference.
USB is most likely the best scheme for you.
As others stated keep ambient electrical noise to minimum avoiding for
instance dimmers, etc.