Gee, lots and lots of things. It doesn't have a HDD, and doesn't have an IRDA interface. The processor is not nearly as fast as in the empeg either. There is no USB, and no serial interface on the box (although there *may* be one inside). There is a version of DisplayServer for it though :-) (saw that at the European meet). Sound output stage is different - the receiver will actually drive a pair of speakers. I'm sure there are a few other differences too, but can't think of them right at the moment. I'm sure someone else will jump in, or maybe you could ask on the receiver bbs

(list 6284, Mk1 S/N 00299 4GB blue [for sale]. Mk2 S/N 080000094 6GB blue)