I'm thinking about adding an amp to my system and would like to stay under $1000. I'm currently using a Marantz sr7007.

What are your opinions on the Marantz mm7055?

The MM7055 is a very good amp in its price range, however I think it would be only a marginal improvement over you current SR7007. Check the measured power output for each here,

Comparing the SR7007 with 5 channels driven, the MM7055 is only 22 watts more at .1% distortion, and 10 more at 1% distortion. The MM7055 would probably sound a little more refined, but not more powerful. If you replace your current speakers with some of a lower sensitivity, them you will want more power. Every 3db drop in sensitivity of the speaker is like cutting your power in half. Suppose you have 100w on a speaker with 89db sensitivity, then you will need 200w on one with 86db, or only 50w with one at 92db. Each scenario will have the same ability for loudness and dynamic range.
Start looking at digital amps. There are some very good ones out there that sound very musical and offer gobs of power for the money...