I wish they would create a report on room sizes. for speaker placement and how many.
I have a room 11.5w x 15,5 L and 8 H
just wondering as currently I only have 5.2 with QS8.
However just seems I am missing that rear sound channels.
I am 10.5ft from front speakers and back wall is 4.6 ft
but, I got a rear entry door and it is 2 ft off the side wall.
Many die-hard Atmos people will say, "Get your base (bed) layer right first, then add overheads."
So a solid 5.1 (or 7.1) setup is required first. You should have that +/- and room acoustic or speaker placement issues.
Get the side surrounds down closer to ear level to offer greater separation from the overheads.
If going 7.1, actually push your side surrounds just slightly in front of the seating area. If staying 5.1, put them just slightly behind the seating area.
15.5' from front to back wall is not really lending itself to a change from 5.1 to 7.1, but it depends more on how close to your screen you are sitting. I had a 10' x 15' room for v3.0 of my theater, and 5.1 was plenty, but my seating was also against the back wall and looking at a 104" screen.
From there, you want to basically make a "box" around your seating area for the overheads with 2 speakers in front of and 2 speaker behind your listening area.
Here is Dolby's 5.1.4 recommendation.
Here is Dolby's 7.1.4 recommendation (which real world has shown could just a touch of modification, like side surrounds slightly in front of the listening area.
And here is a modified 9.1.2 layout that I did up based off of Anthony Grimani's recommendations (look him up if you wonder who he is). He really likes a 9.1 setup with just 2 overheads (9.1.2) over *most* 7.1.4 layouts, but again, your room isn't that deep at 15.5 feet, so you probably don't have the big gap from your main speakers to your surrounds. I added comments about how he suggests a 9.1.2 layout (in red) vs. Dolby's 9.1.2 layout diagram. He says surrounds no more than 1-2 feet above ear level, but in the video that I watched where I made my notes, he was talking about rooms with 10 foot ceilings, so lots of space between the side speakers and the overhead plane. That is why most will say to put them "just above" ear level for Atmos.
Now, I can go on and on about monopole speakers only, but if you went 9.1.2 for a layout, you could put the QS8s in the front wide spots and get a pair of overheads and a pair of new (monopole) surrounds. Keep this in mind though. There is no (ZERO) native Atmos content for a 9.1.2 layout, but you can upmix into it, and that works really well. You will end up upmixing everything you watch anyway (trust me).
But, if you want the maximum match up of speakers to native content, then you need to find a way to add 2 rear speakers, and 4 overheads and get to 7.1.4. Again, that all depends on your seating location, how much room you have behind that location for the rear surrounds (and overheads).
Don't leave out DTS:X either. Might as well plan for it. Basically, DTS:X, whiel super flexible, likes the overheads further away from the seating area than Atmos. Heck, it is allowable to have them up where your front and rear walls meet the ceiling, but that is outside Atmos spec.
If you look at the angle recommendations from Dolby for how far in front and behind your listening area to put your overheads, if you put them closer to (but not at) the further distance of their recommendations, you will be within Atmos spec AND hit a nice sweet spot for DTS:X content.