I didn't think I could fit more than 6.1 in that room due to the sliding door in the back so close to the wall, half-bathroom and fireplace plus it's not wide enough to accommodate 3 side-by-side chairs and still put speakers to the sides. I had a 6.1 system for 12 years and then I started experimenting with a set of front heights when I read that Yamaha AVRs had a "dialog lift" feature for many years and I found my existing AVR already had it (and frankly the rear center speaker wasn't used for much and often sounded "in front of me" due to a psychoacoustic phenomena so I could use them instead and it would switch at a button if I needed the rear channel. I just had to try it out so I wired up those bookshelf speakers on the top of the bookshelf.I have a 5.0 system because that is all I have space for, I can't even fit a sub in.
OMG, what a difference for the Yamaha DSP modes that sounded like little more than just an echo box before. I suddenly had dialog coming directly from the screen (instead of under it) and with the movie theater DSP mode, a mono movie like The Maltese Falcon sounded like I was in a giant old fashioned (not so dampened) movie theater. I was sold on the dialog lift feature, but kind of disappointed it only worked in those DSP modes, all of which seemed desperate to change my room into some other kind of room. The giant room effect was kind of neat, but I didn't want it for newer movies.
That's when I came upon the idea of using a mixer to make my own effect (and that would give me back the rear speaker full time as well). Along the way, I discovered someone made a 7.1 decoder plugin box that could use my 7.1 Input Mode (the AVR had 7.1 speaker support, but it came out before TrueHD and DTS-HD MA so DTS-ES 6.1 was as far as it supported for discrete decoding, but it had a 7.1 input mode for future decoder upgrades. It was pretty cheap (<$100) and so I tried it out with speakers sitting out in the room just to see what it would do. It turned out, it worked pretty well in that little nook before the bathroom and so I used that for awhile.
Then, I read about Atmos and figured, why couldn't I just put another pair of speakers below the existing surround speakers mounted high on the side walls and I'd be set for 5.1.4! But since I was ordering so many speakers on eBay, I found out the PSB X1T speakers were narrower than the T-45 model they were a newer replacement for and it would just fit in that corner without blocking the door (not great against the wall, but the room EQ would help as could sending bass to the sub instead) and there was no reason I couldn't mount the PSB CS-500 speakers on the ceiling (one screw only needed into a joist). The next thing I knew, I had 7.1.6 worth of speakers in the room.
By then I had read about adding extra speakers to an existing 7.1.4 AVR so I went for it. The one I ordered had front wide support too so back to eBay and now it was 9.1.4 (but I could only run 9.1.2 or 7.1.4 at a time). I read about a high-end AVP that added extra speakers using internal mixers and I figured I could use another active mixer to simulate front wides and make it 9.1.6. I also read about "Scatmos" (a term to indicate using Pro Logic decoders to extract a "center" channel from any two signals sent to it, so Front Height Left + Rear Height Left = Top Middle Left and with a 2nd processor, I had support for top middle speakers that sounded discrete. I was at 9.1.6.
I remembered how well those speakers worked in the nook by the bathroom (I had added the towers in the back so they were repurposed) and I found another pair and put them there with another active mixer using side + rear signals and I then have my current 11.1.6 setup. With all the active mixing, it took some tweaking to get the arrayed phantom images to line up right, etc. with where a real speaker would be and aligning the main phantom with the real front height, etc. so everything became "holographic" (It still sounded good with movies along the way). Now, the only thing to do is replace the 11.1 AVR with a 15.1 or better yet a 17.1 (if they ever offer one) to have true discrete 17.1 instead of partial plus mixed arrays and decoded extra channels.
But I never in my life thought I could squeeze 17 speakers and a subwoofer into that room and have them align in any kind of correct pattern, but I guess I was wrong. I've got room for a 2nd sub (could help even bass out for the 2nd/3rd rows a bit better) beside the fireplace (I'd stick that fake fern on top of it and it might not even look bad).