Was about to get the same psu/case (TT soprano) still getting the case becuase of great cooling ( 2x120mm, 1x90mm) and decent looks (ii hate the look of sonatas)
I decided to pick up that case without psu and chose the antec smart power 500 watt (modular, dual 12v rails with 33a total, antec branded)
rods comment about the soprano psu was false. That is not the same psu. Heres a pic of the specs of the psu with the soprano case.
Soprano PS
18a on +12v, which will hold up your system fine, becuase you chose not to have the SLi mobo. If you plan to OC, get something a litte more powerful, like the smartpower.
I also noticed you metioned the xion 2 case, has pretty much the same cooling as the tt soprano, almost the same psu. heres a pic of the specs
Xion 2 psu
Personally I would choose the TT over the xion. If you really want to be sure about your power, choose the soprano w/ no ps, get something like the samrt power listed above.