I've never had a problem with sibilance out of my 150. That said if you're looking for the ultimate center channel with that system, most people will tell you the best choice is to use the same center as the mains you're using.

So three M22's might be the best set-up for you if you can accomodate it under your screen.

My Stuff :

M80's
QS8's
VP150
EP800
Denon 4802
Emotiva XPA-3
Samsung BD-P3600
Sharp 65 Inch Aquos LCD