Careful here. There are two different things being discussed.

The "internal; midi (slave mode), remote (only the start/stop operations are controlled by midi messages received from an extrenal midi device) and auto(master/slave settings are switched autom. : it becomes slave when it receives a start message from a external midi device)." stuff refers to the way the Boss will react to external clock and start/stop messages.

This is nothing to do with "syncro start" as found on arranger keyboards, which I think is the feature you are looking for.

I don't think the Boss will auto-start in response to a keyboard depression on the master keyboard. To start the Boss from the master keyboard you will have to explicitly send a "Song Start" message.

Could start/stop the Boss using a footswitch? At least this would free up your hands!