I too have a DR-770, and use the individual output extensively. Sometimes, if I have a song with many dynamics, I not only use various drum kits, but duplicate each pattern I created, recording the track via MIDI about 20 times, each with a different sound coming out of the indiviudal. Then, I apply the desired effects, and bounce them down to two tracks.
As far a drum machine goes, selection depends on what you are looking for it to do. I've been happy with mine, but a friend of mine hates it. He swears by the DM-PRO, using his 770 just for the touch pads.
Your best bet is to spend some time in the music shop playing with them. If the guys who work there won't let you do that, fine; just find another music store to deal with from then on.