If your mains wouldn't be too far apart and you probably would get away with a phantom center however a center speaker is desirable so you can adjust the volume depending on which movie your watching (some movies have the center mixed to low and need to be raised).
The M80s have their bottom woofer very low. The M60s is higher but I don't know if it's high enough. Then you have the M50s as suggested. Good luck.
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Bruno
M80s/VP180/QS8s/EP600/AVR-890
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"The problem is choice..."