David, the code referenced in @JDC's post (link) starts at line 1678 In the Sonos Advanced Player driver code. Simply modify the two lines with the yellow highlight so they read:
String evtSub = MRRC_EVENTS
String callback = MRRC_EVENTS_CALLBACK
Then click SAVE. It's a large driver so it can take a minute to compile, but once the circle stops spinning you're ready to go.
