Design Spark PCB is a software program with a huge device and components library syste, It has SPICEcapability to test the circuit before you ever place a component on a board. The different libraries are supported by all the standard numbering systems and compponent names. I took a brief stroll through it the other day and found that at my experience level it could be an asset for me. It uses modular blok and allows multiple voltages and different power supplies. It also has the capability to enter the data for a new component or one not listed in the huge set of multiple libraries to set up a system withh SPICE to check it's operation. It's about a ten minute sign up and down load and if you use Picaxe or basic chips they have 2 additional libraries that can be added too.
WCB

Sounds interesting, I have not found an off the shelf high voltage digital pot board to incorporate into the I2C control system yet. A custom built board looks like the best solution to that problem, and incorporation of the other IO chips onto the same board would simplify things.