As Tony says, this has come up before at least once. The answer is almost certainly that neither Ethernet, nor USB, nor IDE in an Empeg has DMA hardware, and that the current best-case transfer of about 700Kbytes/sec is thus CPU-bound from all that PIO. However, I don't remember writing anything in the car-player that disables USB when Ethernet is active, or vice versa, so the Jemplode folks could possibly try it out without any player changes if they really, really wanted to. There could be other reasons it won't work, though.

Peter