Dolby® (a pioneer in the world of surround sound) has a really great interactive tool for determining speaker placement in a 5.1 or 7.1 setup. Here's the link . . .
We offer all of our in-wall and ceiling speakers both in pairs and as singles. Here's why a single in-wall speaker exactly like your front left and right speakers is often your best solution . . .
Cabinet-style speakers often include a port (opening) that is intended to improve the bass performance of the speaker. HTD incorporates a transmission line port design that is significantly better than other speakers in our price range . . .