Can you build out an angled section of drywall, make it look stylish (extend it across the whole wall or something) and then use that to mount the in-wall 150 ? You probably need some extra mounting thingy to stop it sliding out/down of the frame though...

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8