Just to verify that we're working in the right direction, can you see any errors on that port, either from the empeg or switch side?

Also, it weird, but it appears as if 3Com has removed almost all refernces to the SSII 3000 from their web site. The only place I can find it is some apparently leftover stuff from their old (blue, before the interlocked rings) web site. It's almost like they disavowed any knowledge of that switch. Which is not totally amazing, as memory of the problems I had with it come flooding back. You might want to see if you can update the firmware. The only page I found is this old SSII 3000 Software Library page.

You might also want to try forcing the switch to full duplex. I doubt that the empeg is full-duplex, but I don't have any way to test here, and it can't hurt any more than it's hurting now.