I went with the Pioneer VSX-21THX...just yesterday as a matter of fact. I compared it to the Denon 1910 and the Yamaha 765 and found I liked the 21 better. I feel the mid range was a bit more defined and "warmer"...yes I know that is a word starting many an argument but that is how it sounded to me and my wife...who seldom notices such things but is becoming a more learned person in this area hehehe...
I did my auditioning at two different BB Magnolia's in Syracuse NY yesterday because neither had all the receivers I wanted to audition. I wanted to hear the Denon 1910, Pioneer 1019, Yamaha 765/665 and others in this vicinity. The speakers I used were a pair of Klipsch towers and Martin Logan towers for variety. I also used my own demo cd for music as it has a very nice mix...to me anyway...of music that I am very familiar with and tests both speakers and receivers, etc.
I felt the Denon, while very nice, emphasized the lower registers a bit more and the Yamaha's the upper registers a bit more than the Pioneer did. I made sure all the receivers were set up the same and the volume levels were the same...no I did not bring my spl meter...I'm not that big a geek hehehe. I did not test any Onkyo's at all as I'm not interested in that brand.
I have a Yamaha 659, have had it for 3 years, and am familiar with the sound.
I really liked the sound of the Pio 21 and felt it was well worth the few bucks over the Pio 1019 and the other brands I auditioned.
Set up was fairly easy but I would suspect not so for someone with no previous experience installing and setting up HT gear. I thought the manual was well laid out and quite clear. I honestly did not even use it until after I installed it and connected my peripherals and began to set it up. It was quite easy.
I love the sound, in my ht. I noticed immediately how much more defined and "warm"...yep there is that word again...the sound is compared to my old and well loved 659. Dialogue was a bit more clear and defined, which honestly surprised me as I thought the 659 did a fine job. Highs were not quite as bright as with the 659 but, imo, have a nicer sound.
I'm no expert by a long shot and have no handle on the correct terminology but am using words that seem right to me...
I was very surprised at how much better a BD movie sounds when using either True HD or DTS HD...I did not expect much of a difference and though I am a big forum fan I just did not expect the difference I experienced compared to non True/DTS HD formats...the depth, clarity and range really surprised me and I was shocked when my wife...who would be completely satisfied with the speakers attached to the tv...said she loved the sound and could hear things she did not hear before...WOW.
So after spending several hours listening and comparing I felt the Pio 21 was the best bang for the buck and sounded the best, again only to my ears/and wife's, compared to the other brands/models I listened to yesterday.
Good luck and keep us informed.