I have a pair of Sierra 2's and am eventually going to go for a 7.1.4 setup once my new home in finished. I'm also thinking of upgrading them to EX. The living room area is 20' x 17' with a 120" screen on the 20' wall. The ceiling is vaulted with beams.

I've been thinking of getting 8 HTM-200 SE for surrounds and heights, which would be $1,200‬.
There's also the option of getting 4 Lunas for surrounds and 4 HTM-200 SE for heights, which would be $2,900‬.

I don't know how the Luna's would compare as surrounds for an extra $1,700‬, as that's quite a bit of money just for surrounds if it's only a marginal improvement. I'm open to other speaker ideas too for heights if HTM-200 SE don't work well on the ceiling.

As far as the center goes, it would have to be placed under the 120" screen and angled up, so it wouldn't be at the same ear level as the left and rights. The Horizon's height is 11" while the Sierra 2 (on its side) is 7.5". I'm not sure if the Horizon would sound better in this setup.

Looking forward to feedback