The 663 looks like a 661 upgraded with HDMI v1.3 and internal decoding of TrueHD/DTS-HD so all reviews of the 661, especially as a preamp, should apply to the 663. If you don't need hi-res decoding, look for a clearance sale on 661s.
The biggest preamp difference between the 805 and the 663 would be Audyssey room correction, IMO (ignoring the extra HDMI input). It's not a trival difference in some rooms...almost unnoticeable in others. The 805 also offers THX post processing modes...again, some love 'em, some hate 'em.
Just to tease you a bit. If you analyze this purchase for a little while longer, the Emotiva, Outlaw, and Sherwood-Newcastle prepros should be shipping...how many months has it been since you first started asking about the 805?
-Brent