I'd look at keeping the speaker count on the low side in that small, reflective, room. Luna for the surrounds would be my choice, just to keep the base level consistent in tweeter-type. I might also take the opportunity to lower the surrounds 6", or perhaps more, but do some testing before deciding on the final position.
You might also consider some additional toe-in on the front speakers, to improve the coverage area, given that your seating is more to the sides of the sound field.
Instead of investing in more speakers, I think your best option going forward would be to invest in some room tuning devices. Some absorption on that front wall, for instance would probably result in a much cleaner sound. Contact GIK Acoustics (or similar company) and let them design a set-up for you to best take advantage of your speaker investment. Design services are free.
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Last edited by RayGuy; 02-10-2020 at 12:46 PM.