Ok, following the steps in section 12 of the IQaudIO manual (http://www.iqaudio.com/downloads/IQaudIO.pdf) I found that on page 26 it recommends using alsamixer to set “PCM” to 86% (for approx 0dB output; 100% would be +6dB), and to set “Playback” to 100 and “Playback Boost” to 100 too.
I did all these, and the sound is closer to what I would expect for a suitable output.
I still expect it to be a little louder, however, so I set the PCM to 100% and it seems about right now.
And are you able to set these values as default for the DAC+ for future max2play installations?
Out of curiosity, I was hoping to add a hardware volume control to the DAC+ – would it then be adjusting the PCM value in ALSA, rather than the Squeezelite volume?
Is it possible to set SqueezeLite to use the PCM ALSA mixer for volume control from a SqueezeBox remote app?