There shouldn't be a problem getting Hijack to display the ADC values it's seeing (more useful than the resistances) with an interface like the Button Codes Display. It's just a matter of writing the code...

You could write a player replacement that does nothing except listen to the tuner port (/dev/ttyS1, I think) for stalk command packets, and display the values it receives - there's sufficient documentation in the Developer section. I think there's an incantation for /bin/od to print out stalk packets - we just need to adapt that to dump them to the player screen. (Then you bring the empeg back indoors and move the real /usr/bin/player back into its rightful place).