In HUI mode it just sends lots of various midi commands every time I press a transport button
e,g, play gives
controller 15=14, 47=68, 15=14, 47=4
i.e. a protocol
Pianototeq just waits for any activity on a certain controller to initiate "play standalone"
Say I tell it to listen to channel 15, when I press play on transport it will play, then stop a second later because of the 2nd control 15 value
It also has a MMC play option, but no joy.