actually, the collectors are tied to ground, and the emitters to the supplies. the speaker connects to ground, and the center tap of the floating power supply. and there's also two versions, one with the collectors on the supplies, and one with the emitters on the supplies. if you analyze the diagram below, you will see when the top transistor is "on", both output stages have the left hand terminal of the load at a more positive potential than the right. QSC's main technical reason for this odd output stage is that it can be driven from low voltage driver circuits, because the base drive for the outputs never goes much beyond +/-1.5V
QSC usually has a detailed troubleshooting guide in their manuals because this "backwards" output stage throws people for a loop.