5 1/2 months late on this reply but...
As of last week, I'm now using the setup you were asking about. Adding the 770 to my setup has definitely improved the bottom end when listening to music and movies. I'd also say that dialog in movies is a bit clearer, for whatever reason. When playing at somewhat louder volumes than I really find comfortable, the sound with the 770 is certainly more full--the 4802 had a tendency to sound a bit thin to me.
With the dynamics of the room I'm working with (sunken living room, open on two sides, hardwood floors) adding any punch to the bottom end was a positive for me, so I'm very pleased right now.