The filter board has been designed to be completely integrated and controlled from within the Midibox SID software. Therefore there is no need for potentiometers of any kind and all the information will be presented on the Midibox SID LCD.
Do you have a heatsink on the 7805. If you're feeding it with 12v it's got to dissipate the 7v and considering the amount of LEDS and backlit LCD I would expect it to get pretty hot. As these regulators do have thermal shut down features I wouldn't expect them to last too long without a heatsink before shuting down.