From my limited understanding it sounds like you may have developed an ark between stators. Again in my limited understanding, it sounds like you may have developed a hole(s) in the diaphragm(s) when the popping happened prior was probably the diaphragm sticking to the stator. A good practice...
I haven't heard the PA3, so I can't do a comparison to that.
But my guess is that it would not measure the greatest. It doesn't sound the cleanest even with not so efficient speakers. It doesn't sound bad. If I were to compare it to headphone amps it sounds closer to the Massdrop CTH than...
I had the input to my DX7S DAC paused and could hear the noise. I could also hear it while playing music.
Edit: I switched over to RCA cables (I am using the XLR for my Stax energizer now). I found that it goes away when I have the RCA passthrough disconnected (they are connected to my speaker...
I felt like using earbuds as I have a pimple that my overear headphones are annoying. And I noticed a slight repeated popping sound. I have my 789 hooked up to my DX7s with xlr cables and I was on the lowest gain signal. Any idea what to try to stop it?
You could also go with the JDS Labs El DAC and use your MacBook's optical out (headphone jack doubles as toslink) and pair it with the Atom amp.
But I guess that goes above your price range.
There are quite a few extra models from Stax it sound like Amir owns several. Not to mention that other companies make energizers that will work with Stax, Woo Audio, iFi, Headamp, Mjolnir.
Was thinking that you could use a tape adapter, like:
https://www.amazon.com/Reshow-Car-Audio-Cassette-Adapter/dp/B07FKFMRGF
I guess that would have to be measured though somehow.
The Topping DX3pro would seem to fit what you are looking for well:
https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-topping-dx3pro-dac-and-headphone-amp.4967/
You might want to look at https://www.audiosciencereview.com/forum/index.php?threads/smsl-su-8-version-2-balanced-dac.5433/
It is more than $100 but less than $500