You CAN connect a DAC20 to LocoNet, and have the DAC20 operated using LocoNet commands. Provide it with a suitable DC power feed to SK1 pins 1 and 2, and program CV10=1. The DAC20 will then not expect a DCC input signal and will operate using the "Switch Request" messages from LocoNet.

You may need to connect the board ground (SK1 pin 4) to LocoNet ground. You will need to make a special modified LocoNet cable to do this: simply connect to strands 2 and 5 of the LocoNet cable.