Use a DTMF receiver chip to detect the tones. Feed the PA audio input into the chip and connect the DV output to the PA Mute input. Probably a $5 investment in parts, or a minimal drain on your junkbox :-)
You'll still get a brief burst of tone (20-50msec) at the beginning but the rest of the tone will be muted.
Gordon S. HlavenkaTragically, as many as 9625 out of every 10,000 individuals may be neurotypical