Batboard

OK, I know the topic is probably on here already but anyway. I need to take flat audio from a XTL1500 we are using as a base set and pipe it into the station PA. I noticed on the accessory plug a pin for flat audio out. Which other pin do I use to make the circuit to the PA input?

audio gnd

although any ground will work.

I thought so but wanted to make sure. Thank you very much.