Denon AVR1708/3808 vs Onkyo TXSR575/875 matchup? ?

I don't know about those models, but I do own an Onkyo TX-SR605, which can be bought on the www for around $400.

I haven't used the Audyssey EQ because my room acoustics are excellent. I've made all the adjustments manually and it sounds great.

But what I wish to convey is that the sound quality of this unit is sensational in view of its price. That is to say it competes favorably with purist high-end amps and preamps in sound quality (and I've heard plenty of those and own a few myself).

I feel no need or compulsion to add a tube preamp or a better amp section, or anything of the sort. This thing sounds great just the way it is. It kind of freaks me out how close it comes to my 2-channel (much more expensive) purist systems for such a cheap price. And the multi-channel surround modes are marvelously enjoyable.

If I were to be extremely critical I could say that the upper midrange sounds just slightly thin compared to my expensive gear but I'm using cheapo cables on the Onkyo and it's really just starting to break in. Its midrange smoothness, excellent bass articulation and crystalline extended highs cannot be denied, ignored, or otherwise swept under the rug. For those just getting into this hobby, buying the Onkyo and some competent speakers would be a great start in my view.

Sorry I cannot compare to the Denon. I'm sure they are very good too but do cost a bit more for the same performance level as the Onkyo according to my research.

Plato, thanks for your response.
Question?: what ways are you running the Onkyo? Are you running digital connection (thus processing PCM in the Onkyo - if you listen to CD's at all?), describing DD/DTS -master receordings w/Digital connection? Do you listen to direct analog connecions from other sources?
I just want to know how you've been using it.
One thing I'm thinking, is that the Dolby -HD and DTS Master processing is obviously a big step up in processing other than listening to old DD/DTS out, analog out of an old DVD player!
Please specify, if you would? Thanks.

Funny thing is I bought the Onkyo 805 for HT but for 2 channel listenning, in my set up the 805 sounds pretty awesome and I like the 805 better in 2 channel audio than in multi-channel HT . When listenning to clean and bright Etta James " All the Way", the image is huge and clean and vocal is sweet and way better than I ever expected from a receiver. However, with Shirley Horn's cut " The man you were" from " Loving you" CD and Diana Krall's " Temptation" cut from " the girl from the other the room " I was dissapointed since there is some thing missing or not quite dynamic and not quite clear ( not quite sure what it is) from the top end. My 2 channel audio listenning is set up via Digital Coaxial. For HT, the dialogue is also awesome but the top end information again, somehow is kind of weak and subtle and not clear and powerfull as with my Parasound AVC 2500U HT set-up. It seems to me that the 805 is heavily emphasized the mid-range but the top-end spectrum is not quite there. I tried both with and without the Audyssey and still there is sort of over emphasizing in the mid-range to compensate for the shortcoming of the top-end. The unit has been returned to dealer eventhough I really like the fact that the 805 is smoother than the Parasound in 2 channel audio listenning but the 805 does not quite have the dynamic to give me the "being there" effects in HT.