Power should not be a problem. A 20amp breaker would be better then a 15amp one but either should work. I'm running a XPA-5, UPA-2, 2 600w subs, 52" tv and a computer all off the same breaker and I've never had a problem.
If you are only going 2 channel then no need for the XPA-3 amp and the UMC-1 prepro. That would leave you with a killer 2 channel setup. I guess it depends on if you want a 5.1 HT setup that works well for 2 channel as well or just a 2 channel setup. I use my prepro for 2 channel duty and find it does an excellent job IMO.
Hope that helps some.