Hi aadev,
Thanks very much for this information! As it happens, I'm starting something of a skunkworks RaspberryPi project myself. Since I also have an AxiomAir I thought I might have a look at the RaspberryPi in it and see how it works -- including trying to get standard Volumio running on it!
There are multiple versions of the HiFiBerry DAC that work with Volumio. It appears that the one that is most similar to the Axiom DAC in the AxiomAir is actually the HiFiBerry DAC+ Light -- it has no extra hardware volume control. It's not clear from what you've written but the "HiFiBerry DAC" that you mentioned is most likely the HiFiBerry DAC+ Standard, which actually does have its own integrated hardware volume control. With your MacGyver-ed configuration, the problem most likely is that the Volumio UI is trying to send volume control commands to a hardware volume control in a DAC that isn't actually included on the AxiomAir at all.
Just to clarify further, are you saying that based on your current setup you can play music from either Spotify or your NAS on the AxiomAir but only at max volume in both cases?
Have you saved the original image from the AxiomAir RPi card?
And finally, just to be clear, I haven't tested any of this myself yet. I think it would be safe to try changing your Volumio configuration to correspond to the HiFiBerry DAC+ Light and see if that allows you to adjust the volume properly from the Volumio UI -- assuming nothing has been fried in the AxiomAir by what you've done so far, I can't think of any reason why one more minor change would cause an issue.
However, I'm not a hardware engineer! Perhaps Ian or Andrew will be along at some point to warn us of the error in our ways. If not, I'll keep you posted as I get to try a few things myself!
Mike
