Painttoad brings up some good ideas and one potential pitfall. There was a lengthy discussion of the reasons not to use car amps in a home theater last year. Speakers are not nearly as drastically different as amps, but they are designed for a different environment - receivers often have a hard time with loads at or below 4 ohms. Sources such as Parts Express can give you a good selection of speaker drivers intended for home use (easier for a receiver to drive), and there are at least a few DIY'ers around here who could probably help with the design (enclosure volume, crossovers, driver selection, etc). One thing you might try first (if you can grab an extra pair of speakers from somewhere) is mocking the concept up with a couple speakers on temp stands - see what it sounds like while sitting on the couch, and perhaps what orientation works best for spacing and angle.