ER-4PT direct out of a standard mp3 player was really dull.
ER-4PT(S) + 75 ohm cable out of a headphone amp (Yulong U100) really took them up a level, however I felt I could drive the ER-4S just fine out of my DAP, or at max volume out of my laptop.
I never EQ'd them actually, but the razory bass is ill-suited for my electronic music, which often has distorted bass on purpose, and then the ER-4 really just shows that shredded bass to you and it sounds like something is incorrect (when it's not, it's just displaying that information in the bass to you in an uncommon way), so the ER-4S was ill-suited for that, however I still liked them a lot, apart from the fit.
I'd be happy to try the ER-4 again in a custom IEM, which I intend on doing rather soon I think, I think the perfect fit and perhaps eq'ing the bass like you're saying with result in a pretty good sound.
The EX600 btw, I find is leaning more towards razory bass than uumphy bass, it's just borderline razory for me, to be honest I like the bass in the EX700 better, which quite likely has my subjective favorite bass in any IEM, but the EX600 mids are far far nicer than the EX700.
Edit: The EX600 has better sub-bass than the EX700 though, however it has less hmm how to explain this... it has less viscerality.... ugh I hate analyzing the weaknesses of the EX600 I love this IEM so much.