I have finally found a analog IO chip with I2C interface that will support 0-10V outputs to drive 0-10v input proportional control ball valves. The TI AMC7812 provides 16-12 bit analog inputs, 12 analog outputs, and 6 GPIO output/inputs. With a couple more devices like the LTC 2487 from Linear to do thermocouples, a PCA9535 for digital outputs, and a PCA9685 for PWM control, most of brewing applications could be handled with 4 IC's that would run about $30. This is overkill for 99.9% of the systems out there as brewtroller/BCS is all that is needed, but for the terminally crazy automation folks this would open up all sorts of possibilities. I expect the code and calculations to be beyond the Arduino platform capabilities, but with the ARM9 mini 2440 platforms or Raspberry PI platform there should be enough capability to make this work.