Im sorta in the same boat, the whole receiver thing is quite puzzling, however, from what I can gather from my research, I dont think there is a receiver below 600$ that can touch the Onkyo 606. I personally dont think Denon is as good a company as they used to be unless you go into their high end models. Im sure I will get lots of people arguing with me on that, but its my opinion.
I was considering the Denon, but it doesnt do video upconversion/transcoding (not to be mistaken with upscaling, which it does).
I think Sony's are kinda overpriced, again just a personal opinion, I think the same thing about HKs, but they probably have a better quality build that accounts for some of the price hike.
From what you have listed there Id probably go with either the Pioneer or the HK, but have a look at the Onkyo. From what Ive read the main issue with Onkyo is that they run much hotter than the others, but I think as long as you dont put it in a closed door cabinet and give it some room to breath, you'll be fine.
Im currently trying to decide if I should get the Onkyo (you can pick it up at circuit city for 450$) or if I should go to something higher up like the pioneer elite VSX-01, Onkyo 706, Marantz SR5003 or other... anyone got any feedback on this? Its quite a price jump to go to these but willing if it makes sense.