I think the internal effects are probably better than the ones you mentioned as add ons. The Lexicon is the only one of the bunch that I like. I have a 500 and it's soooooo nice.
try this:
Set the internal effects to a muli-delay and use the Lexicon as a smooth, lush reverb. Avoid chorus on the voice and make sure the vocals come out ABOVE the band, the way they should. The audience needs to hear the words - they're not musicians, so they identify with spoken word more. Music soothes the savage beast, but singing gets the girls to swoon !