Noise was a hard problem as well. In the end what helped us a lot was to keep the FX device in its own case and even solder the digi potis right in place where the real potis had been before. You can see that here:
https://im.static-thomann.de/pics/images/stompenberg/backsta...
The relais modules are on the outside of the case, but on the left you will see a flatband cable (digital) run inside of the case, where the digipoti modules will sit. So all analog signals never leave the original case and the metal housing shields all kinds of external interference.
The relais modules are on the outside of the case, but on the left you will see a flatband cable (digital) run inside of the case, where the digipoti modules will sit. So all analog signals never leave the original case and the metal housing shields all kinds of external interference.