I just got my VSX-1121 set up this weekend. I replaced an Onkyo 809 with it because for the last 3 months I was chasing my tail trying to get the sub set up properly in my room. If it wasn't for the bass issue, the 809 would have been a perfect receiver for me. BTW, my speakers are all 4 ohm Emotiva 6.2/6.3/ERD-1 running in a 5.1 setup with an Elemental Designs a2-300.
With that being said, here is comparison of the Onkyo 809 vs Pio VSX-1121 in my opinion. This is intended as an aid for anyone considering either of these two receivers.
Onkyo 809 seems more refined in sound quality. The receiver seems to push these 4 ohm speakers more effortlessly. The sound stage in my setup was much better and almost seemed higher end. The 809 is rated at 25 or so more watts, but I haven't seen a bench test for it. The vsx-1121 was benched at 80+ watts per channel with 5 channels driven I believe. Bass management was a nightmare to get right with the 809. Tried running Audessy literally 50-60 times and still had issues with it bottoming out my sub, boomy at times, etc. The vsx-1121 only manages sub timings and levels, so it was easier to integrate my a2-300 into the mix. The 809 is clearly the winner to me with my setup at this point for sound quality, but I just couldn't get the sub right.
EDIT: Crossover setting on the Onkyo are at 10hz levels, the Pioneer is much more limited with only a few that jump 50hz at times. (50, 80, 100, 150, 200) AND you can choose different XO setting for Front, Center, and rears. Much nice
The video processor in the 809 is far superior to the one in the vsx-1121 in my opinion. There are much more tweaking options and presets with the up conversion on the 809. With the vsx-1121 you only have the option to turn the up conversion on or off. Much simpler for someone starting out, not so much for anyone more experience or who likes to tweak. I use the up conversion on and I see no real change on my setup. With the 809 I clearly saw the changes. Miss that a whole lot right now. 809 is clearly the winner on the video side of things.
Remote, build quality, aesthetics
Remote: Onkyo's is MUCH better. It is contoured so you know you are picking it up properly in a dark room. The Pioneers is a perfect rectangle. So you sometimes aim it upside down if you don't look closely. Button layouts are much better on the Onkyo remote as well. Onkyo wins here.
Build quality: Both units are nice and heavy. The Pioneer is all plastic up front. The Onkyo has an aluminum face plate. Pioneer has a nicer display in my opinion. Onkyo is rather plain. Not a big deal. Onkyo is roughly 10 pounds heavier. This is pretty much even.
Aesthetics: overall, the Onkyo looks like a better built, higher quality unit do to it's aluminum face plate. Navigating with the just the buttons on the unit seems easier to me on the Onkyo. Th GUI is much cleaner on the Onkyo. Pioneer's is so old fashioned it's not even funny. The internet radio/DNLA features are FAR superior on the Onkyo as well. Nice clean colorful display on your screen. Pioneer is grayish background with white letters. Ridiculous this day in age. Lastly, the through option so that the receiver can be off is AWESOME on the Onkyo. All you can turn off are the speakers on the Pioneer, so the unit has to be on at all times. LOVE and REALLY miss that on the Onkyo at this point. Onkyo wins hands down!
In my opinion, with my setup and in my room, the Onkyo 809 is the overall winner. Although it is a bit more expensive, you get more features, better sound quality, better video up conversion, nicer remote, and a better built unit. If I could have gotten my bass management to work properly, I would have kept it. The Pioneer will stay for a few weeks so I can tweak it some more, maybe add an external amp to power my fronts and center to see if I can get the sound quality I'm expecting and experienced with the Onkyo. If not, I am going to try something else. Hope this helps anyone considering both of these units.