either will work fine. I use a Denon receiver with my RC-70"s and it sounds great. A speakers impedance can fluctuate at different frequencies but the RC-70s are very easy to drive even with an entry level receiver.
Will you be adding a subwoofer or more speakers later?
I would probably get the x2000 over the E400 for $50 more. Better version of Audyssey and longer warranty.
For a sub I recently got a Polk PSW110 for $80 at bestbuy but it feels pretty underwhelming to be honest with you, i'm thinking of returning it and save up to get a SVS SB1000 in the near future.
I also have a set of Energy RC-10's that i'm planning to use as surrounds but will need mounts to hang them on the wall since they are pretty heavy. The only missing part would be the RC-LCR which is very expensive right now, and the RC-R which are impossible to find
I don't think i'm going to ever finish building this sound system, I will eventually have to buy a separate amp and processor