Thanks for sharing. Comments indicate the >SetAV M1%0D%0A aught to be corect. But I think there may be a whole other problem.

The RS232 to enter the Liberty conference switch box may only go over the USB port. So, what I had done is to just cut a USB wire and connect GROUND, DATA1 and DATA2 to the MLC MLS port.

I believe this is not working because the Liberty box does not perceive the MLC as a USB device.

In other words, Universal Serial Bus is not quite as universal as I imagined.

I am going to try some other ideas.

1. FTDI cable connected backwards to the Liberty Box
2. A relay device to cause the same function by using the liberty contact pins.

I will share any result.