Mainstage return/back communication.

Hi,
I'm building a USB midi footswitch controller which I'm going to use with Mainstage. I succeeded with all the programming. Well almost. I have a problem with communication from Mainstage to my MIDI controller. I know there is a possibility to recieve updates from mainstage about parameters I'm controlling with my MIDI device. (I use also nanokontroll2 which works like that - it's recieving LED's updates from mainstage).
Maybe some of you know what type of messages I should sniff for. I'm even not shure if these are midi data or more specific SysEx.
Maybe there is a way I could sniff my USB connection from MacOS or directly on Arduino.

I will be thankfull for any help or advice.
Thanks.

OK,
it's solved!
I used MIDI Monitor app to monitor midi USB data that comes back to Arduino. Basically it's the same command as you send to Mainstage and you assigned to a button. It just differs last byte from 127 for "on" to 0 for "off".
It was easier than I fought.