What's important in a budget HT in wall speaker??

I have decided to keep my 2 channel music and multichannel HT systems separate. I will be using 5 identical in walls for the HT, don't want to spend a huge amount. The room is about 4K cu feet. What are the important characteristics for these speakers?? My guess is that clear treble for voices/effects and a cost effective subwoofer (Hsu maybe) would be the way to go. I will likely use a mid range AVR, maybe get a cheapie amp down the road if I feel I need to move more air.

I have some Paradigm AMS 150s in the ceiling of my bathroom driven by a sonos integrated. for $150 off ebay, they sound pretty damn good. i was thinking of something from that line.

Any suggesstions??