You can have multiple processors controlled by 1 interface. Just designate in the button properties which processor to trigger or if the button is in standalone mode, create a "macro" on the processor in question and use that system macro within your buttom macro.

Sell an RP6 everytime. There is little reason not to especially if the components are installed.

You may try for direct IR control of the projector by reflecting off of the screen once it is down. This is hack but it works sometimes.