I've heard connecting multiple USB cables is a matter of audio quality/jitter concerns. I know independent labs measured it high. I use a Mac mini as a music server and there was a question of which port to use for audio. Most said the USB port closest to the A/C outlet was preferred as this would eliminate "noise" in an aluminum bodied Mac mini. Personally, I didn't notice noise, regardless of USB port used. Of course, I use a DAC.
But Apple seems to have eliminated audio quality/jitter concerns with the release of the current/uni-body generation of Mac minis.