I have not seen your room but given that you have exposed beams, how much do they protrude past the plaster or drywall? If it is more than four inches, the ceiling could be built out between two of the beams that would create a space sufficient to accommodate a inwall speaker with an integral back box such as a Perlisten, as well as create a space to get wire across the ceiling for the speakers. Great thing about such a speaker is that you can get pretty consistent performance expectations from them. Just a thought.

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