Can someone assist me in understanding QSC's grounding scheme in their RMX amps?

This circuit is like a bridge tied load with the speaker placed between P1 (the output signal) and the C120/ C121 junction the speaker return path.
Usually a BTL has both sides driven but in this case only one side of the bridge is driven (P1). The junction of C120/ C121 supplies a passive ( 0VDC) between the supply rails.

P1 is connected to A1 and GND through R20/ 6R8. This is more of a Low level path rather then any high current related to driving the speaker.
 
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