Well been studying up on the finer points all summer. I have my room layout graphed out, I have mock up paper cutouts of speakers and tv hanging on the wall, I have located all the wall studs, and thought through all the wiring routes.
ROOM / LAYOUT
Room is vaulted ceiling bonus room, F & R walls are 15 ft long, and 13" apart. Couch needs to be up against back wall. Upper part of ceiling is 9 ft. As mentioned, the Front and rear walls have attics behind them and are only dry-walled on the inside face.
I will locate the 55" TV about 34" from the floor so that seated eye level is about 25% up from the bottom of the screen, 75% from the top.
Center channel will go directly below, maybe 3-4" space between the two. Both are centered on/between two studs, which are almost middle of the wall.
L & R will be 2 stud cavities away from TV; one empty cavity between them. Ideally I would separate them a bit more, but since the seated distance from the TV is less than 13 feet, this should be good, and keeps the L & R within ~20 degrees off center from viewer. Also keeps them away from an attic door on the left and the computer desk on the right.
They will be slightly higher than ear level, however I am going with speakers that have aimable mid/tweet components with 18 deg of movement. Should be able to dial them right in and down to my sweet spot.
Rears can't go in back wall (too close to couch) and one side wall is an outer wall, don't want to mess with that. Actually I think the best option and best sound will be in the 45-degree portion of the ceiling above the couch. Spread out not too far, maybe halfway between the center seat and the outside L/R walls, also using aimable mid/tweet components so can aim mostly toward the couch. They will end up about 5 ft above my ears and 5 ft to either side.
I have an older 6" Infinity powered sub in the room already; this will complement the new speakers and we'll see how it does. Can always upgrade (or add another!) later.
Now for HARDWARE SELECTION....
Bought the TV earlier this year, its a 55 inch Sony Bravia KDL-55700B smart tv. Best Buy for $800, and I gotta say it looks terrific, haven't even calibrated it yet. It doesn't have the fastest processor, but plenty of options and is almost too large for the room. Wife would say definitely too large ;-)
As mentioned in OP, gotta go with in-wall speakers due to space constraints with the room being multi-purpose. The more I studied the options, the more I saw that there seem to be tons of open-backed in-walls, at reasonable prices. And there were some Enclosed in-walls, a few were VERY cheap and then the high-end enclosed. I ruled out the open-backed types once I studied the recommendations above and the sound science behind them.
I did not want bottom-market enclosed either... Luckily I have a friend who is a Monitor Audio dealer and can offer me some deals. I did like the SoundFrame series (SF1, SF2, SF3) which can be configured to mount IN or ON wall (this appealed to me since mounting ON wall is easier, and more reversible down the road). But even at dealer cost these were more than double my original budget.
So I looked at the CP Controlled Performance line. After tons of research and talking with my dealer buddy and the Monitor Audio rep, I took their advice and decided on the CP lineup. I finally placed an order for
Left/Right: CP-WT380IDC x 2
Center Chan: CP-WT240LCR x 1
Going rectangle for the rears!: CP-WT260 65w x 2
And the L & R are backordered!!! Grrrrr...... Having them wait on the entire order until they can get it all at once, don't want to risk getting half the set and not the L & R for some reason.
Even these speakers at dealer cost are a few hundred over my original budget. But I am ok with upselling myself, after not finding anything that I was happy with for less.
I also picked up a 100w Denon AVR-X1000 5.1 factory refurbished from Accessories4Less. Price was good, but first unit had a bad HDMI card and would not send any output to the TV. Sent it back and got another with little drama, so only temporarily annoying.
The LRCs above are rated for 100 watts and the rears for 65w, so this should be about perfect for 5.1, and more than enough for my smallish room.
MA estimates mid- late-August for my backorder. I can live with that as long as they don't keep pushing that out. Meanwhile I think I am safe to hang the TV on the wall, I don't think there is anything that could change my mind about where that will go.
I can cut the holes for the wiring and mount those faceplates to make it look nice. One behind TV and the other behind computer desk, wires running in attic unseen.
Then when the speakers get here, I will be able to get the center channel in first, centered with the TV. Then the L & R based off those. Will be a snap to run the wiring from the computer/AVR desk to those via the new wiring channels.
Running wiring to the rears will be a bit more complicated... They will also enter the attic space behind the front wall, and hopefully up and over the vaulted ceiling, to the rear attic space. Then just up into the ceiling/roof space to the rears in the 45-deg ceiling.
I enjoy designing and executing this kind of stuff myself, but do rely on others with more experience for guidance. I find myself pushing my comfort zone limits a bit, and so thank you for participating in this forum and sharing your knowledge!