PTT on 6600M but using Maestro - not working

I have the 6600M under my desk and using the Maestro as main console to avoid clutter on the bench. I plugged an RCA PTT footswitch into the 6600M as I want the freedom to grab the Maestro off the bench to traipse around the house. The foot switch doesn't work. I get an error message that I need to select a slice on the 6600M for Tx. If I do that then I get side channel audio from that slice on top of the Maestro slice. In Settings, Transmit > MIC2 PTT is disabled. I switch it back and forth but no difference. If I choose a Slice for Tx on the 6600M it works but I think that will mean Tx is dependent on the 6600M slice and not the Maestro, right? Is there any way to resolve this other than plugging the footswitch into the Maestro?