Re: 1st post: Splurge on a 73" Diamond or go with the lower end model?
I'm not up on the Mitsu TV's, but I suspect either TV will outdo what you currently have, and the Denon 3808 will allow you to switch HDMI, and take advantage of the new high res codecs available on Blu-ray (which you need as well to really see what your new 1080p TV can do).
Given the new model comes out in a couple weeks, you will need to decide first if you can or are willing to wait that long. Do you have another TV that you could use until the new model? If so, wait and look at them both and see what you think, if you buy the cheaper one, maybe in a few weeks you can also save up for a Blu-ray player and have the whole rig done in one shot!
Ken Taraszka, MD