Yes, the DJ Shield pots are form a voltage divider between 5V and 0V, just as pots are typically used in Arduino projects. The Arduino reads the input with analogRead(pin).
The buttons on the DJ Shield and the two buttons on the Audio Hacker connect the Arduino input pins to ground when the buttons are pushed. digialRead(pin) returns HIGH when the button is not pushed, and LOW when it is pushed.
Actually, would I have to make major changes to the code to add more SRAM chips? I can get the ones you use pretty cheaply. I’m thinking instead of 256k memory, maybe expand it on a new shield to double or more memory.