Just ordered 10 Stereo jack sockets from a chinese seller on ebay for about $6. I would have liked to use switchcraft sockets, but they're above $5 EACH :S
Next step is the 6-channel digital potentiometer. I'll be using an AD5206BN10 chip.
This chip includes 6 individual digital 10k pots, with 8-bit resolution (256 resistance steps). I think this should be enough, considering it's essentially 40 ohm steps. If i want to emulate logarithmic pots (for volume) It might not be enough though... We shall see.
Most other parts I already have (Arduino nano, single colour LEDs, Hammond 1590BB enclosure, various resistors) so once I order the digital pot chip I should be good to go
I might have to look into a larger enclosure though, i'm not sure if there'll be space for 9 jack sockets and power (4xTRS for expression pedals, 4xTS for In/Out for stereo volume, 1xTRS for expression pedal input) but we'll see, i'll mock up positions of components once I get the jacks.