Was the firmware the standard Benbox one, something like: LX-Nano.328p.20150626.hex?
I don't think you can reverse the axis with the Benbox firmware, so you'd have to change the motor wiring.
See what it does with T2Laser now, if it is Benbox firmware it will still work (although not all functions are available).
If I know the required pinout for your machine it is simple to compile a 1.1e hex so you can use T2Laser, if you are interested.
Also, one more question. Did you try the 0.9j custom firmware?