Analog Synth Interface: wheel reinvent avoidance

Howdy My goal is to make a laptop interace for my ARP2600. I have a pretty decent MaxMSP UI going, and am ready to think about the best way to send out the juice. MIDI is an obvious choice, since the controllers are so nicely organized, but that might be more retro/baggage than is really necessary...maybe straight serial would make more sense. In any case, the ARP has a lot of ins (>40), so to get discrete control over each I'm going to need three Arduinos, looks like. Are there ID issues with plugging in 3 via USB to a single laptop, or can the cpu distinguish between them easily? If anyone's done any synth interfacing, any advice most appreciated. The goal is to use MaxMSP to a) send audio into the preamp of the ARP b) override the sliders into each of the modules with laptop mousing. The ARP runs on a 10 volt scale, so ultimately the Max data will have to scale to 0-10V.