I've got touchkit working on my Mac (just today actually). I have a Xenarc 700TSV and I'm using the drivers from http://xenarc.com/driver-touch1.html
According to Xenarc's website, it's Version 1.10.5214 (04/14/2006).
I don't know if you could use this version with a different manufacture of screen and honestly I don't know MacOS all that well (I'm a Windows sysadmin) and this is my first mac...and it's going in the car.
No idea about upgrading the firmware - it can't be done with the Xenarc's without swapping the board.