Kappas are said to have very rich mid range. Probably best speakers for the money. Came directly from their home speaker line.

I had 5.25 coax's in the rear of mine and 6.5 components in the front (diamond audio). It sounded fine. I don't think the rear speakers need to be fancy. They're just for fill. I usually set the fader to bias the fronts... to the point where I can just start to hear the rear and leave it like that. As for the sub, I usually set the cutoff so that it overlaps the rest of the system a little and then set the volume at the point where I can just start to notice it's there. Once you have the system dialed in like that, it sounds good with the volume around mid level and up.