I've spoken with Denon Tech support several times and they confirmed that the 4306 does not support 1080P - only 1080i. It was some time ago but I thought at one point there was an option for me to pay $500 or something crazy like that to send it back to Denon and they would upgrade it to support 1080p - but I thought that was crazy expensive so I did not do it. I can't find any details on that at the moment but either way I don't have budget to do any receiver upgrades.
I ended up ordering a Sony BDP-N460 and a Digital Optical Audio cable to go with it. I'm waiting for it to arrive.
I'm a little confused by your comments. If I plug the HDMI from the Blu-Ray into the TV so I can get 1080P picture, then I plug the Optical Audio into the Blu-Ray and out to the receiver to pass the audio (including the internally decoded Dolby TruHD, I should be good right?
I'm thinking if I go HDMI direct from Blu-Ray to Receiver and try to pass uncompressed LPCM over the HDMI I'll get the audio, but lose the 1080P.