The AVR-5805 has so many more additional features than the RV-8 it's hard to put it in the same class. Our measurements indicate that the quality is exceptional as well in terms of amplification and pre-amplification use.
There's really no comparison - though some would take a Lexicon over another brand simply because of the name and reputation.
I suppose if you don't want/need HDMI switching/upconversion, IEEE 1394 inputs, 4 zones, 10 channels of amplification, Audyssey Room EQ, 2 additional component video inputs, additional digital ins and outs... you get the idea.
