Just added a sixline two weeks ago to my tank with yellow tang, clown, lawmower blenny and bengai cardinal. He's one of my favorite and the others don't care he's there - though they all have territories the sixline is allowed in all of them.
He's eating very well after a day adjustment period. Flakes, pellets, mysis, brine shrimp, zooplankton so far. Hasn't yet touched the flatworn. I only have one.