Wow! That sounds like a wonderful system. I am very interested to hear your more detailed review of ALL of your Axiom products!
I'll bet the Denon will be just fine. You'll likely get unnecessary upgradeitis eventually, anyway, so you might as well save some stuff for later.
I don't think the bi-amping is going to do anything for you since all the channels on the Denon are sourced from the same power supply.
For those short runs, 14g wire is just fine. I do like the look and feel of 12g, though.
I'm a very happy URC MX-700 user. That model is discontinued, but both the wife and I really like it.
You can always add another sub or upgrade to the 600 or 800 if you feel the need. I bet that - after you get the 500 positioned and dialed-in - you won't feel the need. You may feel the "want" though.
If you don't already have a UPS for the DVR and PC, I think that's a good ~$100. My hand was forced by the bulb in my RPTV, but I like knowing that I can shut the hard drives down gracefully, too.
Congratulations on your new home. Warmest wishes to you and your family for many happy years there.
