This is because the BraVo only has one IO (GPIO) and it takes two IO´s in order to control the up and down motion of a screen.
Also the BraVo does not have a bi-directional RS232 port, so feedback from the projector e.g. lamp hours is not possible.
Instead go for the Neets Control OsCar as it has 2 IO's, that is if you still only want the 4 buttons, or of course you could go for bigger control systems as well.