Sorry to resurrect an old post, but I'm having similar issues to the OP but I'm quite new at this so I'm not sure if I'm doing anything wrong. Basically I'd like to figure out a way to control my Bose M1 Multi Room Interface device with serial commands and I can't seem to get that working testing with my PC.

Currently I have a CP2102 USB to UART converter connected to my PC running Windows 10; on the other end I have the TX pin connected to the ring and the GND connected to the shaft of the 3.5mm connector which is plugged into the Serial Data port of the M1 unit.

I downloaded AccessPort to send serial commands given by rjbradlow from the earlier post but the Bose unit doesn't seem to be responsive. I can measure a signal on the 3.5mm connector whenever I send a command from AccessPort so I'm assuming these are going through to the unit.

What else am I missing?