I have been using mine optical in and out. As I reported earlier, I have the pops (which are relatively innocuous IMHO as they are very quiet), as well as the startup glitching. I mentioned that I thought there was a buffering issue, but I have more thoughts since then. Keep in mind that it's pure speculation on my part:
A couple of decades ago, I was interfacing/programming a DSP and I encountered a very similar sounding clicking. After discussing it with the chip designer, he recommended avoiding muting and unmuting unless absolutely necessary. So I added a delay, and voila, no clicks (unless it timed out of course).
I'm guessing the PW-Link has a similar issue, and in addition has a sizable buffer that it needs to process the convolutions. The mute behavior and the buffering behavior are probably interacting to cause the startup glitch. If that's true, the software implementer has the choice between unmuting the playback asap (hoping for the buffer to be full or filled with start-of-track silence) or delaying the playback causing a lack of responsiveness.
What's also interesting is that Tidal played through my Squeezebox has in-between clicks, and Tidal played through the Play-Fi app only has startup clicks. And I don't recall hearing the startup glitch via Play-Fi. My guess is that the Play-Fi app plays better with the DSP's API, and that the Squeezebox implementation does not.
Also, one other interesting datapoint is that I believe a Roon user reported updating his/her player software, and the clicks disappeared.
In any case, I am guessing that a player-side software update is where it's likely going to fix the issue, and that a firmware fix might do things like mess with gapless playback (again a buffering implementation issue). All that being said, I am living with the clicks, as they don't bother me that much.
