I have a B&K 5 channel amp, rated at 200w per channel. I bought two of the mono blocks, mostly for stereo music listening.
I didn't want to fire up the 5 channel amp for stereo. I have Polk speakers, rated at 90 for efficiency, I believe.
Even with these easy to drive speakers, my 18 year old son says he can hear an improvement. Not to mention the improvement for movies, now the B&K drives the center and rear surround.
And remember, you will have a 30 day trail period, if you don't find an improvement.