You are right that Denon has a great rep. But you pay for it. Its not really a coincidence that you are comparing Onkyo's best to Denon's midline. For Denon also makes 4308, 5308, the 09 series, let alone the separates.
I will simply presume that the only listed receiver with torroidal transformers is the Onkyo 905.
Bigger amps = more heat. Reon chips make a lot of heat.
If you like Denon, go for it. I would take the 905 if my speakers enjoyed more current. I think of Dynaudio, Totem (which I guess uses Dyn drivers a lot), or other speaker technologies, such as planars, electrstats, ribbons, etc or particular stuff that has either low minimal impedances, or crazy looking impedance curve, or simply just low sensitivity...
You'll probably be happy with any of them.
I am having a hard time choosing a new A/V receiver. Mine is an old Yamaha which do not have any HDMI connections, etc. Using optical audio output for now, and single HDMI from PS3 to TV for the video.
I have a Sony PS3 and a Sony HDTV.
I am debating between these few receivers:
SONY STR-DA5300ES (great reviews on CNET.Should have lastest firmware. However not that popular with the a/v diehards?)
Pioneer Elite VSX-94TXH
ONKYO TX-NR905 (like the THX and HQV Reon VX. No GUI interface. Heats up easily???)
Denon AVR-3808CI (nice GUI. Reputation for making great receivers???)
Please help. Thanks in advance.