Ken,
Harmony 101:
1) study vocal groups like manhattan Transfer, Four Freshman, Beach Boys, Mills Bros, even nSync. You have to THINK like a group b4 you open your mouth.
2) take all the vibrato off the harmony presets, if it has it. You don't want the backup singers to do anything you DON'T.
3) use dynamics as much as possible, and turn the harmonies on and off alot to emulate a real vocal group accenting certain phrases. Unless it's a trademark harmony tune like "Surfer Girl" or the same...use the backing voices in a supportive role.
4) keep the lead simple when you're singing in a group. Don't bend as much, don't trill and embellish like a gospel singer. Stick to the melody and let the harmony create the beauty and excitement !

Have fun!