Thought I would also join the discussion and make the list as well.
1- 64audio U12t (with FiR Modules) - great detail, separation and excellent timbre, especially for drum sounds. Bass can be tweaked with modules, but it is still amazing (regardless of technology). Easy to listen up top, which makes it great for metal.
2- QDC Anole VX - detail oriented signature, great imaging and a very fast IEM. Can get a bit fatiguing for long periods.
3- VisionEars VE8 - best timbre in the business for vocals and instruments. Might not be the most impactful in the bass region, but definitely one of the best IEM out there.
4- Sony IER-M9 - great reference IEM. Quite neutral with decent bass to round things up. Excellent for vocals and imaging.
5- Campfire Audio Solaris - Not the best bass in the list, but this IEM feels very coherent to me (except for that upper mid dip). Fit can be an issue for some, but does most things very well (especially the lower mids).
6- Empire Ears Legend X - Does not need much introduction. The king of bass (in terms of quantity at least). Detail might not be its best trait, but it’s a fun IEM to listen to regardless. Pairs really well with modern music.
7- FiR Audio M4 - Excellent bass and quite relaxed up top, which makes this IEM very pleasant to listen to. Overall, I think it’s the best bass I’ve ever heard (better than Z1R imo). Unit variance is a real thing though, so better be careful !
8- Sony IER-Z1R - Very popular model and I can understand why. Too v-shaped for my own tastes, but lower treble and bass are its best assets. Comfort can be an issue too, so better to be safe and try it out before buying it.
9- 64audio Tia Trio - Sounds too v shaped for my tastes as well, but has great extension on both ends. Mids sound a bit hollow and too far back in my opinion.
10- Shure KSE1200 - Best resolution in the game, but has limitations everywhere else. Treble is WAY too hot for me, but can be good for well recorded music or acoustic. Bass is alright at best.