Oach, take it from someone who has actually done what you have suggested.
I have a NAD T743 Receiver (50 watts). I bought two Outlaw Monoblocks for the fronts. Sound improvement (or difference) was quite easy to notice especially for movies. More dynamic and more full. My girlfriend noticed immediately and she had no idea what I was doing (so much for blind tests!). I know the science and math on decibels and watts and I don't really care. It sounded better at the same volume and this should be your reason for getting them. Do not get these because you want louder because the science is correct, it will not make your system that much louder. Athough, I don't know the specs on your Yamaha - just guessing.
The monoblocks are an inexpensive, modular solution. I believe they are comparable to products that cost a few hundred more.
That said, I just bought a stereo tube amp and I'm thinking of selling the monoblocks for extra cash for a new player. This is not a sales pitch. I'm actually thinking of getting one for the center channel also.
And if the presumptuous people have anything to say about that I have one message: get over it. Its a hobby and I can easily afford it.
