Share my experience. I have DIGI+ on my Pi-3 running Volumio latest version, streaming to JOBSYS Integrated amplifier via SPDIF, which encounters exactly the same behaviour as you, got a “pop”/“click” sound between tracks playback WAV or FLAC up to 24 bit 192kHz. I think it is the JOB detects and locks down the digital signal. I do expect it happens between album of different bit depth or sampling rate, but definitely not between tracks in same album of same format. Using the same source setup, this issue has never occured on my previous DAC/Amp Hegel H80.
I changed to use the USB instead of SPDIF output of Pi-3, and it resolves the “pop”/”click” sound in between each track on playback PCM. However, I still encounter the same behaviour on DSD playback. I found an article google.com.hk/url?sa=t&rct=j … -E9H4fL1SA explains why there is “pop” for DSD playback.
The suggested solution is using some music player software like JRiver v19 which can handle the DSD output level change between track. I have tested JRiver and Foobar2000 on Windows10, both did not notice this behaviour. However, in term of sound quality, I prefer Volumio. So I think I will wait for its next release which hopefully will resolve the problem.
Though I am using Linux or Windows (sorry,… I’m Apple hater), hope my experience helps the support team to understand the problem, and improve in future release. I believe it is not hardware problem on DAC, it should be caused by the software.