One dimension I didn't see yet is how far the listening position will be from the LCR speakers (and from the screen). That is IMO the main determinant of how big/beefy your LCR speakers need to be.

Room dimensions probably would help as well... we are probably all guessing something like 20-ish x 20-is x 10-ish but we could all be wrong.

Another vote for investing in center channel and sub.

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