If it's a 10/100Mb/s auto-switching hub, it might drop down to 10Mb/s when it sees the empeg, including the traffic between your desktop and the rest of the net. Meaning that there's more congestion, and all traffic is restricted. Which you notice more with your music uploads because they're long and busy (and because you can't wait to hear your new music ).

Putting your player onto a different switch means that you're not restricting the one attached to your workstation, so the traffic between it and the rest of the net isn't affected, and only the traffic to the empeg has to go through a 10Mb/s switch.

I'm no network guru, though - that's just what I picked up from other discussions here.