Can you get HD Audio within your setup?
Short Answer: YES!!!
I am not sure about using HDMI for just the audio and component for video, if that works, that is the best possible setup in your case to get the losless audio...however
If you purchase one of the new Sony models such as the s550 or the Panasonic BD55 that supports up to 7.1 analog outs and internally decodes all the new hd formats, you can run component cables from your blu-ray player to the television for video and run analog cables from your Denon's Ext. In to the analog inputs on the blu-ray player.
You will be able to enjoy all the audio formats such as Dolby True HD, DTS-HD that are supported by the blu-ray format
The only downfall to this setup with analog cables as opposed to using HDMI is bass management is limited because it defeats the bass management of your Denon receiver. Usually the crossover is fixed at around 100.
You can not use optical or digital coax to get the new audio formats because they can not handle the higher bitrates of DTS-HD and Dolby True HD. You have to either use HDMI or a series of analog cables.
Note: I do not think the BD55 suports 480i so when you are picking out a player make sure it supports the 480i resolution.