You have a beautiful HT! I have a flat ceiling so my plan is to go for straight in-ceiling speakers. I'm seeing some great prices for Polk 80 F/X LS (~$370/ pair), which are supposed to be timber matched to the LSiMs. I only worried about the angle, on the polk forums I saw a few threads talking about them, but not a comprehensive review about them.Looks like a good setup! I have LSiM 705's up front with a 704c center, 703's as side surrounds and 702 FX's in the rear and they work great together! I use an Outlaw 5000 to power the LCR's plus 2 front height speakers. For atmos, I was using Focal Sibs for awhile (on ceiling or on wall mounting options) and they were ok, but not great. Because I have taller ceilings, I was able to build some little speaker stands out of 2x4's and plywood and mount 703's as rear surrounds and I have Polk Legend 200's setup for the front heights and they sound amazing! Not sure if it would work, but maybe you can get some Polk Audio 265 LS in wall speakers and mount them in ceiling. They have an aimable tweeter and the tweeter matches the LSiM line.
From what I have read the in-ceiling if that can be done is considered the best solution, thats what I'm trying to find a couple pairs for.I have a similar setup and used Polk TL3s for my Atmos speakers, mounted with omni-mounts so that they could be pointed at the MLP.