I’m likewise sensitive to problems in the upper-mids and lower-treble, particularly with snare hits, so I can offer a couple of suggestions for you. First, beware of some dynamic driver IEMs: the Dunu Zen is too emphasized in this region, as is the Sennheiser IE 900 (I’ve not heard the IE 300). I’ve not heard it but my impression from reviews on forums is that the JVC HA-FDX1 IEMs (sold by Drop) likewise has some emphasis there.
A just-released pair of affordable IEMs that seems to be promising is the Moondrop Kato (a DD IEM, ca. $200). The Kato has received lots of praise on SBAF and one of the IEM aficionados on this forum, Precogvision, has some quick impressions of it here, which you might find worthwhile.
I’ve not heard the B2 Dusk. I found the Satsuma uneven in its frequency response and a little prickly at times.
The SA6 is a great pair of IEMs. The bass is excellent, it extends pretty deep but has a nice, hearty mid-bass presence that I’d say works well for bass guitars. I had no problems with its upper-mids/lower treble. I very much liked it and would consider buying it if I were in the market for IEMs in this price range. Its main drawback, for me, was an overly thick, weighty sound - and I should emphasize that I say this coming from my favorite IEMs, which are the Andromeda 2020, which provide a much lighter, more ethereal and nimble, fast, and responsive sound (even as they have plenty of mid-range emphasis).
Another excellent dynamic driver IEM that has nice mid-bass emphasis and is free from upper-mids/lower treble nasties is the Oriolus Isabellae. I prefer this over the SA6 for its tonality, timbre, and engaging qualities, although the SA6 bests it for technicalities and sub-bass extension. I’d recommend that you read one of our forum member’s review of it here on head-fi. I agree entirely with his take on the Isa.
The Andromeda 2020 is a wonderful pair of IEMs. It has the right combination, for me, of technicalities (resolution and speed, especially), and tonality and musicality. It also makes for a fatigue-free listen, and I love its incredibly open, spacious soundstage (for an IEM). It has six main limitations: first, it’s quite dark in its tuning. If you want more treble sparkle, get the original Andromeda, now called the “Classic” and available here. Second, it doesn’t have the best slam and macrodynamics (although this is mitigated with finding the right, synergistic pairing with DAPs and amps). Third, it places an emphasis on the mid-bass region and doesn’t extend very deeply into the sub-bass (which may not be an issue for you - as a bass player, you might like its tuning). Fourth, all of the Andromedas are very sensitive and can hiss from the wrong sources (I’ve not heard it on a hip dac). Fifth, the Andromedas are also reactive to differences in output impedance from sources: below an ohm, they get bassier and darker (there’s a risk of the 2020 getting too dark), above an ohm, they get brighter. Six, the soundstage is wider than it is deep.
One last suggestion: if you don’t mind buying used IEMs, the Campfire Audio Solaris is excellent and can now be had second-hand for $700, if not less. They were $1,500 when new (they now sell new for $1,300 here). Unlike the all-BA drivers of the SA6 and Andros, the Solaris is a hybrid combination of dynamic driver as well as BA ones. This means that it improves on the Andromeda 2020 in a couple of key ways: it has more slam and stronger macrodynamics; its bass response is better - faster, tighter, and it extends further down into the sub-bass region - but it’s not a bass-head pair of IEMs; instead, the bass is well integrated into the overall tuning; finally, the Solaris takes the lovely open, airy, and spacious soundstage of the Andromeda and adds more depth, making the overall soundstage more holographic. It also retains the speed and nimbleness of the Andromeda and adds more resolution (to my ears). Its tuning is closer to neutral, and it’s not dark like the Andro 2020.
The OG Solaris is not a perfect pair of IEMs, though. The shells are large, stick out quite far, and can be uncomfortable for many people. It’s too blingy. And it’s even more sensitive, I think, than the Andromeda, so beware of hiss. (Note: the Solaris 2020 solves the problem of shell size but has a different tuning and is too bright and fatiguing for me, including in the upper-mids and lower-treble regions).
If you opt for the Andromeda or Solaris and the hip dac doesn’t pair well with them, the Lotoo Paw S1 dongle synergizes exceptionally well with both, and it should be quite affordable now that Lotoo is releasing a new, updated version (I’ve not heard the new one).