There are in-walls available from Paradigm, B&W, M&K, Atlantic Tech, Boston Acoustics, and a number of others. Dane settled on B&W's, and this thread of his might be handy reading for you. Paradigm has recently added to their in-wall line (I've got a set of Paradigm Studios at home, so I can't leave them out ), and M&K and Atlantic Tech are both well-regarded speaker brands.

I would seriously recommend considering bookshelves for the mains if possible -- you'll have much greater flexibility in positioning for optimum sound. All of the brands above offer good looking bookshelves. From the description of your space, I understand why you are looking to use in-ceiling speakers for surround duty -- I think I read something somewhere on a speaker from Atlantic Tech that was designed mainly for in-ceiling installations. Also, if there is a local shop (or shops) that offer any of these lines, definitely demo them at the store at least; even though there won't be a 950/7100 driving them, it could be very informative. Also take some of your own demo material (music and/or movies) with you, so you are using material that you are familiar with.

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