Hi my friend,
Franckly, the FH9 can really to be at the best TOTL level :
1/ you can tweak the vents (shell : overfiltering). Value 250, 3mm : here for instance :
https://fr.aliexpress.com/item/1005004052480882.html?af=171752&afref=https://www.comparedaddy.com/search?q=golo.com&source=1451866&zid=3w9YSu8erqsPd9&cv=12&dp=12::171752::1c0248dkk1e7::::1699006466&cn=15643&aff_fcid=8275acc84ea64468ad6933bd659bd5da-1699006467042-07743-Y7bAZbY&aff_fsk=Y7bAZbY&aff_platform=aaf&sk=Y7bAZbY&aff_trace_key=8275acc84ea64468ad6933bd659bd5da-1699006467042-07743-Y7bAZbY&terminal_id=a4baf7b1327f4bb0b62b495ee83360e4&afSmartRedirect=y
2/ For the aforementioned filters, impregnate the membrane with an indelible marker (black because it's prettier). This stiffens the membrane. Even best bass quality.
3/ For the canula, green filters
4/ For the cable, try absolutely the Ares S 8 wires or best, the Eros S (Effect Audio). It's just ridiculously incredible, sound wise (ergonomics remains very good, as the stock cable). Really. Must try. I insiste.
5/ With your DAP, if you can set the digital filters, try the "minimum phase" filter = a little "analogue" touch. The fh9's love that move very much !!!
6/ About the tips :
https://www.amazon.co.jp/-/en/CWU-GECL-Eartips-Isolating-Prevent-Enhanced/dp/B0991RL358?th=1. These are the perfect tips for me : everything. Problem solved for years, from now on. And every pair is long-lasting (Nothing in common with the Xelastec for instance). But...
you need to fit them...
So it is far less pricey than an another pair of iems, and really... you have already a TOTL level product in your hands.
I can say that because I have compared these "FH9 Dsw tuned" with quite a list of said "TOTL".... (Kr5, XE6, Infinity mk2, A8000, Z1r, Zombie Max, Erlkonig, Phoenix, VE7, etc... to name a few).
All these products are good to very good... but not a problem at all for the "FH9 Dsw tuned"...
Well, I haven't listened them yet, but the
Sound rhyme DTE900 seem to be incredibly good... Or the
Monarch mk (2... 3 : same).