Post edited.. It seems the 600i may not be to blame for these "popping" sounds whilst skipping tracks using pcm audio, I have not tested Dsd yet.
Regarding the "pops" people can hear when switching tracks with their 600i's if listening to Pcm audio (standard windows audio, not asio/wasapi)...
I have found that leaving the 600i at its default 48Khz 16bit, which is the 600i's default playback audio setting in Windows 10, makes the "pop" distortion sound more pronounced and causes further delay between track skips.
Changing to 44.1Khz, to match the source material, which in my case I assume is 44.1 in Spotify, makes the "pop" sound less Pronounced and track switching appears to be faster.
Any sample rate above 44.1Khz, upsampling Spotifys tracks, is causing a loud "pop" between track skips.
If anyone who has a 600i can hear a "pop", between tracks, whilst listening to 16bit 44.1 Pcm material, try changing the sample rate in Windows 10 to match. Is the "pop" quieter?
I tested with a Chord Mojo, which was set to 16bit 44.1Khz (I had it set that way to match Spotify), once I reset it to its defaults (48Khz in Windows 10), I found it behaves the same way whilst using Optical. The major differences between both Dacs, is that the Mojo is connected via Optical, and the 600i is connected via Usb and they both seem to do it. Neither optical or Usb seem to be responsible.
I wonder, if this normal behaviour? I didn't notice it before I got my 600i.
Aside, just a general question for all 600i owners, has anyone experienced a faint "pop" after playing a youtube video clip? After approx (edit - 3 seconds) of silence I hear a faint "pop" from my headphone. I have tried disabling all usb power suspend options. It doesn't happen using optical, only usb. I have tried all "Usb steaming mode" settings, no difference. Windows 10 x64 1709.
Serial number of 600i : 10300500679 , Qc check 2018.02.03, Revision v6.F3