RMB, the best center would be to get a matching M60 for the lower bass that you mentioned. I will guess like many of us this is not an option so unless you are willing to buy the VP180 for a more perfect tonal match, any other speaker will be a bit of a compromise.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70