Ok room is 15'6"w x 21'L x 8'H

I am sitting 13ft from the front L/R ....6' from the rear Backs and 7.5' from the sides.
I watch movies is 95% of the time, normal tv broadcast for major movies and sports.
I have MK 750's for the front three ........ what are the absoluet best options for my rears and sides. These 750's have wicked disspertion detail and clarity should I go with 7 of these all around ? or maybe three across the front and two rear backs and two QS8's or all QS8's for the surrounds.

I prefer Quadpolar design like the Qs8's versus Di/Bi designs. Also not a fan of bookshelf speakers for surround duty, unless you listen to a lot of multi channel music. Some like the rears to be bookshelf speakers.

yeh, forgot the QS8's were quad. Not music is always 2 channel

I'd go 4 QS8's for surround duty.