I had a Denon 4806 that I used only as a digital pre/pro (replaced my Lexicon MC-1).  Although I liked Audyssey, etc I replaced the 4806 with a Bryston SP2 and have never looked back sonically.  The SP2 is just more musical.  Although I have a separate two-channel preamp (a couple of them actually, Bent Tap and Modwright SWL 9.0 SE) I used the dedicated separate analog 2 channel portion of the SP2 for a pre for awhile and it was quite quite good.  In fact, very good, and only bested by my current 2 channel rig.  Says a lot for a "throw in".  Bryston spends a lot of time explaining that the 2 channel pre in the SP2 is basically a BP-26 chipset, and I believe it.  I got the SP2 for its musicality while playing 5.1 analog bypass (hi rez stuff) but even the digital DTS and Dolby processing sounds better than the Denon, IMO.