I like the set up of the QSC and the easy adjustments. I don't know much about the STM or if its even adjustable.Yes but the set ups may be different. As far as it fitting it will fit
X2!No, the primary's can not be interchanged. The Rage 6 uses a short stem secondary and the QSC uses a long stem secondary. It's about a 1/4" difference if I recall correctly. Kris can jump on and give more info.