All good choices for a reciever, and all were on my list. If you like the soundof the Onkyo then spend the extra cash and get the 800, it's got more power and of course THX certification. Not mention some nice audio perks like DTS 24/96 and "pure audio" circuitry. The Kenwood may be the best value of you're looking for mostly movie watching, but I found the sound a bit compromised in stereo audio. But you lso get THX for under $500 really nice, again, for movies.
For me, my ears and my space, I chose the HK AVR525 and am truly in love with it. Do a search for "h1pst3r" or "HK" or "AVR525" and you will find many of my earlier posts on this wonderful reciever. There are many features to this receiver which made it THE choice for me and I elucidate on this points in earlier mails.
For speaker choice I had tried the Polk RTi38s, Castle Acoustic Richmonds, B&W 602s, Boston MicroSystem8000, and FINALLY bought the some of the best speakers I've ever heard: the M&K K-7s across the front sound stage...amazing and they're $250/pc and can be had a bit cheaper.
If you buy the AVR525 (or any other receiver) do yourself a favor and take your time auditioning speakers.
If yo have any additional questions about the HK or the M&Ks just ask!