Yes, the only difference between the 7700 and 7500 is the 7700's two extra amp channels.

You will certainly here a difference between the 1070 and the 990/7700. How much will depend in part on your speakers (more efficient speakers will have less need for the extra power, which will determine just how much difference the separate amp makes). Whether that difference is worth $2000 is a matter of some debate, with no right answer. I really love the sound of my 990/7500 setup (with Model 200's driving side surrounds) and would probably have a hard time accepting the change stepping down to a 1070 would represent, but I still remember how nice my old 1050 sounded - once you reach the level of a 990/7700 you are well into the realm where each upgrade is a matter of diminishing returns.

We have no word on upcoming products, but I'd expect the next generation to include HDMI v1.3, which will take some time for Outlaw to include - late summer would seem to be the absolute earliest, and even that is probably a stretch. Granted, that's just me guessing, but it's the best guess I can make...