USB slave chipsets are generally awful, and USB has a lot else that eats into transfer time - this is why USB is slower than ethernet on the empeg.

The ethernet chipset has 16-bit wide access to it, a decent amount of buffer, and generally is happy with saturating the wire (it doesn't on the carplayer due to some mmap bugs in linux 2.2 - these may be addressed in a future release which will give more speed over ethernet)

Hugo