same here, but i collected speakers and amps mostly. after while found it pointless keeping them cause i never used them cause i'm type person like to find something that work as an ''all-rounder'' for me and keep a pair/set as a back-up.
i never used iem's so i wouldn't know how they are, but i been using pair of stax sr-202 with lambda pro pads and find them very nice sounding and appreciate their effortless approach. they are really transparent in transients but only complaint i have with them is i wish it had bit more upper mid to lower treble and tad more air and they be perfect. i find them to have nice bottom-end impact despite the complaints i see when involving stax cause they work insanely well with electronic music and hip-hop/trip-hop.
Try changing your source. The sr-202 are quite open with very good upper mids from my setup
I agree with your statement about the low-end though , since the sr-202 are known to be the bassier cans in the lambda family.