The general concensus SEEMS to be that the 150 would play a bit louder and possibly offer an enhanced dispersion pattern useful for viewers who are well off-center (like my Uncle Floyd). Someone correct me if I'm wong, but I believe that since both the 100 and 150 use the same 5 1/4" driver as your M22s, either one should be voice-matched to your existing speakers.
The size of the present or future television is not as important as the type of material you enjoy in your home theater and the size of your room. If you like it REALLY loud or have a particularly large room, the 150 MIGHT be a better option for some. I think that your comment "I love the system overall and has plenty of volume for our setup" pretty much says it all, considering the difference between the 100 and 150 would be very small if you are currently happy with what you have.
