hhg,
Welcome to the forum and thanks for providing such a detailed diagram.
What you have sketched out is an
Atmos 5.1.2 configuration click on the provided link for more precise placement advice from Dolby. In this room, given the stair/partial back wall, I agree with you on forgoing an attempt at a 7.1.2 configuration (i.e. with rear-surround speakers). In-walls for all speaekrs, except the Atmos speakers, is a good idea given your stated constraints. Personally, I would lobby emphatically with the "boss" to allow the front three L/C/R speakers to be either bookshelf speakers on stands or at least on-wall, instead of in-wall.
A couple points-to-ponder are provided below:
NOTE: all L/R references are in relation to being seated on the couch facing the screen.
1) FYI: The
diagram's left and right speaker labels are backwards; i.e. the "left speaker" (front or surround) should be in relation to the listener's perspective, not the reader's perspective.
2) Consider
moving the left Front and left Atmos speaker a bit towards the room center (away from the attic access/return air wall) to place them more symmetric in relation to the seating location. Your ceiling construction may allow or impede this advice (unknown to me ATT).
3)
Consider pre-wiring three sub locations; the one you show to the right of the screen, another one on the
left side of the screen, and another one in the
back right corner of the room on the side-wall (~ under the speaker labeled "LS"--which is actually the right surround speaker).
When you get a chance please provide a diagram of the vertical speaker placement to get a sanity check on this aspect of plan.
Cheers,
XEagleDriver
