Right now, I run a Mac Mini which is connected via USB to my DAC. I've tried playing my files off the internal hard drive, an external WD Firewire drive, and an external WD Thunderbolt drive. All 3 sound different, even though I use the memory play function of Pure Music. Go figure ! I liked the Firewire drive the best.
I also briefly compared this with a spare Mac Mini I bought second hand. That was better in every way on paper (faster CPU, 16 GB RAM vs 8 on mine, SSD drive). I didn't like the way it sounded. But to be fair, the previous owner was quite messy with his software, lots of redundant programs, a dual boot partition etc.
When I was using a Squeezebox to stream music, I wired it directly using Cat 5 ethernet to the router. There was distinct difference between two of the ethernet cables I had on hand.