Hello! Have owned and used the XM4's for about a month. I can't recall what led me to this site and thread, but I'm glad I found it, as it's been a wealth of information.
I bought these after several instances of almost buying the latest Bose Quiet Comfort model during layovers, then deciding that I should really do research before such a big (for me) purchase. Most current reviews seemed to agree that the Sony XM4 IEMs were "the best", and I liked the features plus the promise of good sound, so went with them. Looking back, the description of the sound in a lot of those reviews was fanciful, bordering on ridiculous. (Which is maybe par for the course? This is the first audio investment I've made in quite a while.) You all seem to have nailed a more accurate description of the sound.
But I do like the sound. I would sum it up as rich but polite. It does not seem too dark to my ears. As others have pointed out, it is a sound I can listen to for hours without fatigue. In fact, I wonder if the rolled-off high frequency signature is a deliberate way to make sure that in noisy environments, listeners' eardrums don't get tired or damaged. For me, pre-pandemic when I used to fly somewhat frequently, I'd find myself cranking the volume up almost to max on my iPhone with non-noise-cancelling earbuds and ending up hearing almost nothing but piercing highs.
Having said that, this thread has opened up possibilities of experimenting to improve on the sound, at least at times when noise cancelling won't be of paramount importance. I now have some Spiral Dot tips on the way and will try others recommended here -- likely Spin Fit CP 360, ePro EP01, and Symbio Hybrid. Been also experimenting with the Sony app's EQ, and with the EQ on my MacBook via Music. Depending on the music, sometimes I boost the highs, but I also sometimes turn up the bass.
I find myself using these more often than I thought I would -- for instance, during a recent road trip in a nearly empty and uninsulated rental van that would have been torture otherwise. I could insulate myself (mostly, if not completely) from the rattling and grumbling and actually enjoy my music. Have also been taking calls and using them for online meetings, which I didn't really consider when shopping. The only complaint from my listeners so far was during that van drive, but I do hope that a future firmware update improves the microphone sound, if possible.
Overall I'm really happy with them, but trying to resist this rabbit hole of even better sound. (I did not know that Walkmans were still a thing in 2021 and am intrigued!)
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