In case it helps others:
Set DAC to DIGI+ Pro but needed a PI reboot for it to be recognised.
If I knew more I might mod the dacs.json file with;
** ## {“id”:“hifiberry-digi2-pro”,“name”:“HiFiBerry Digi2 Pro”,“overlay”:“hifiberry-digi2-pro”,“alsanum”:“2”,“mixer”:"",“modules”:"",“script”:"",“needsreboot”:“yes”},**
Further to the above I have found a reboot did not always solve the problem. Looking on the HiFiBerry website I found the problem could be that the PI’s audio had not been turned off and config.txt could need that instruction. The info was here:
https://www.hifiberry.com/docs/software/configuring-linux-3-18-x/
My resulting config.txt now reads like this and seems to be reliable.
config_DigiPro.txt (308 Bytes)
Spoke too soon, not working again !!
Now Volumio has a blank screen for Playback Options, something seriously wrong.