Are you connecting it via USB?
If so, you'll need to put the IdPi into GUI mode temporarily or connect to it remotely. The first thing you can try is option 10 from the Id main menu. It might be a bit hard to read, but if the IdPi is finding the DAC, you should be able to see it there. This will just tell you if the IdPi is finding it.
If the IdPi see the DAC, try some of the different output audio devices. If you go to Tools -> Options -> Audio, under Audio Device, you should see several different options, but you should be able to tell which of those options are the DAC. Start with an option that starts with "hw:". You might need to try a few different options to find one that works.