I think the OP has a couple options. We all agree speakers at ear height behind a screen are the best solution. It would seem easy to drop the three prewired speakers lower on the front wall and install in wall speakers behind an acoustically transplant screen. You do not even have to patch the existing holes in the angled ceiling, just paint them blue to match. If I was the OP, that is what I would do and leave the other four speakers up high, angled down.
However, I have been in a couple houses with in ceiling main speakers. It is a bit odd at first but not absolutely horrible. At least his are angled down. You kind of get used to it after awhile. Having the surrounds up high does not bother me.
A far as which in wall speakers to get, it is really hard to demo in wall speakers, for obvious reasons, so you kinda have to go by specs. I don't have time to look up the four options now, but I would look for the ones with a -3dB at below 60 Hz if possible to crossover to a sub, and also ones with higher efficiency ratings so they can get appropriately loud for movies when needed.
I would avoid any sub a custom installer wants you to buy. I get your cu feet at about 2000 (12x17x10), which is not a huge room. There are many subs that can give you great sound in a room that size. Rhythmik LV12, SVS has a couple, Hsu, Powesound Audio. Research some of those Internet direct sub companies. For movie watching, getting a good sub will probably make the most difference as opposed to choosing between Jamo or Episode or whatever for your speakers.