I removed the Roland 531 and a MN Pan Mix to get the PM in the rack. I was going to sell them, but I think I am going to keep them for the utility that sub-mixers provide and the inevitable expansion. ;-) Yeah, I deliberated for a long time before I bought the PM and looked at a load of the alternatives. Ultimately I choose the PM as offering the most bang for the buck with a reputable manufacturer. It is not the ultimate mixer for all racks, but that module doesn't exist.