Mac MA 7900 . How To

Just reset the processor.  It will restore all inputs, triggers, etc to factory defaults.   

https://www.manualslib.com/manual/599507/Mcintosh-Ma7900.html?page=19

Then just turn off the source inputs you don't need and label the ones you do. 

I think page 18 is where you want to start.  Source Input Reassignment