When finding the appropriate center channel to complement the front channel speakers, should I choose a center channel that mirrors the dB level (sensitivity) or the timbre-level (frequency range), assuming that both speakers are the same brand?
For example, should I chose Axiom's VP-100 or VP-150 center channel to match the M60 front channel speakers?
I have been reading that the VP150 is too bright for some folks. I matched the drivers with my center to my mains. Paradigm CC370 with my Monitor 5's. Timbre match is more important than sensitivity match as you can adjust the volume level of any given channel. Perhaps you might try the VP100 and if it does not give you what you need you can always sent it back and get the VP150. If it weren't for the 2 tweeters I would have suggested the VP150 without hesitation as there appears to be a good driver match which bodes well for integration. Good luck.
Like Arthur said - match the drivers when at all possible.
I prefer large center channels or splitting the center and or using a dual center. But...two tweeters and 3 mids doesn't seem like it would be balanced without padding down the tweeters which may account for some of the complaints on brightness, but I haven't heard the 150.
Either center channel will be perfect for the M60 and as Arthur Kyle pointed out, it is good to timbre match the front speakers. You don't want that "gap" in the whole surround set up. Or you could try what other folks have done. Do away with a center channel and go with a "phantom" center, i.e., use the effect of the front mains to provide the dialogue. I haven't tried this set-up but it has been discussed in this forum.
With all things being equal, I'd buy the larger center channel speaker first if added price isnt an issue. Either will timber match nicely, and volume isnt of a concern because you can adjust individual channel levels.