Having now got my DIGI2 Pro and DSP board working, I want to set up room correction. After reading your "Implementing Room acoustics correction using REW" guide, it looked as if using the built-in facilities in HiFiBerryOS would be easier, so that's where I've started.
The first thing that puzzles me is the measurement phase. After connecting the mic (a Behringer ECM8000 + UMC22 preamp), HiFiBerryOS does indeed detect it. After clicking "Microphone Positioned", the system plays what sounds like pink noise at a high level in order to set levels. But when I click "Start Room Measurement" (and the page shows "Measuring room"), there is no audio output to the speakers. This surprises me. I would have expected some kind of frequency sweep (or maybe white/pink noise). I can't see how the the room can be measured without sending a signal to the speakers!
(In case it's relevant, one thing that I observed was that during the level setting process, adjusting the volume made no difference to the level; I had to adjust levels using the amp powering the speakers and the UMC22 input gain control. I'm guessing that this is because I'm using a DIGI2 Pro card, and the volume adjustment in HiFiBerryOS only works with cards that have a DAC?)