I use a Marantz SR6006 as a pre/pro with the 7700. I have used the 6006 without the 7700 just to hear what the receiver had. The results are pleasant, not blow you away great but adequate.
To my ears, with the 7700 my system comes alive.
Played Phil Collins "Live in Berlin" last night and knew I was right there in the audience with this big smile from ear to ear.
You will not be unhappy with the 7700 or 7500 model amp. I purchased a new 7700 but I have heard others on this Forum who purchased B stock and are completely satisfied.