ahender, maybe I missed it, but were you planning on using one of the little Energy speakers as a center channel? I think that would be a bad idea. They might be ok for surround speakers (I'm currently using some small M&K K5 speakers for surrounds). It is very important, however to match the center channel with your left and right mains.

The Sierras will have better midbass than the small energy sub. I'd recommend crossing the Sierras at 60hz. That's what DaveF recommends and I'd trust his word over the "experts" at avsforums.