I've got a 4 Space rack with a QSC RMX850 power amp and a RBI. I've got one more open space and am unsure what I want to put in it. I really want something that can "add" to my sound. At first I was thinking about a rackmount tuner, then I scratched that idea......then I thought about a compressor but I doubt I'd really get much use out of that in a live situation. Anyone have any suggestions for me?