My buddy and I run audio for my church, and we had a great idea to mess around with. We wanted to hook up an external slide fader to a boat throttle via some pulleys and springs, and control the whole house volume using that. With the main output on the board all the way up, is it possible to use a single slide fader to control a whole board's output using two XLRs in and out? If so, what kind of fader would I have to use?
This depends on the board you have. But for arguments sake, yes you can set this up. If your board has an aux channel or a mix bus that is capable of being assigned to (and is not the master bus) simply route all the channels out through the bus to some kind of control unit (maybe even a single channel mixer, then take the output of that mixer, run it back to a channel on the main console and run only that single channel to the master bus. This would give you "remote" control.
However if you are looking to control things remotely there are now consoles you can control from an iPad. This would require a budget and some new equipment acquisition but I have used it on the LS9 and its really cool.