I did the update a few days ago. Was convimced that I didn't have any bass issues as that sounded fine.
However, I have noticed that before the update the instruments were all separated brilliantly and had beautiful crystal clear clarity. Background instrmemts came alive, nothing was over powering it just sounded fab. I've never heard some of the tracks, even on Spotify, sound so good.
Since the update that doesn't seem to be the case. It still sounds good but I feel the background instruments are not as dynamic and appear subdued compared to before.
Would be interested to hear if anyone else has encountered the same?
I didn't know for sure whether I had the bass issue pre-update, it really was confusing as on some IEMs things seemed fine to me, but very clearly, it now transpires that I did have the -10db of bass.
As we have noted, the clarity and instrument separation on the A300 series is phenomenal.
Like you, background instruments on tracks that I had known for over 45 years and had played quite literally, many many hundreds of times, have come alive in the mix, some I had never even heard!
These background instruments remain boosted in the mix post update, but now they have a deep, warm and rich feel with the added 10db of bass.
The only thing I would add and perhaps of note.
On some IEMs, the update had zero effect, absolutely nothing.
On another set, just a mild increase.
On one set however, it was an astounding uplift in quality which totally blew my mind!
Having loved these IEMs for the best part of 10 years, I was so disappointed in them when paired with the A306, that I was about to drop $600-$700 in the hope of finding the sound I wanted in a new set.
Now though, the sound on these IEMs is just as I want to hear almost every track just on Direct, so this owner is blissfully happy with the new Walkman and having a variety of mix options.
Bottom line, I totally recommend everyone tries a few (and very different) types of headphones or IEMs.