SE215 I personally feel it's not too good, back then maybe but not nowadays. And to be honest, the difference from amp is audible, but from mid range and high range amp is subtle, I couldn't call difference. But a good note to yourself, always try to feed good source from a good DAC and also drive the IEM/Headphone well.

My recommendation for 200-400 based on your preference,
Ostry KC06A - 2xx, slightly u shaped sound can cater your needed on emphasis for instrumental
VSonic GR07 - 3xx, all rounder, with slightly sszzz on treble side.
RHA MA750i - 4xx, u shaped, pretty good bass and nicely controlled highs.

Can't go wrong with any of these 

If you want to compare SE215 with KC06A, I would say you'll find SE215 sounds dull, not energetic. SE215 sounds pretty balanced.. the bass is emphasized a little but the bass is flat.. and treble is too controlled, rolled off too fast.

Can check out head-fi website. Most of my info I got from there

Especially the multi IEM comparisons (300+ iems tested)
Didn't hear anything about durability except for the fading Yamaha logo. That's all.

Joker recommended me the EPH-100 as its warm signature compared to V signature of the FXT90.

I'm pretty damn new myself. But one thing I do know is that I dislike high treble, the high notes that will pierce your eye

And I like emphasis on mid range and slightly on bass so that it sounds more lively That's why I went with the warm signature, I purchased the Yamaha EPH-100 which is in shipment to my place already. Can't wait!!

Here's a good guide: http://theheadphonelist.com/earphone-buyers-guide/

You can take a look at the vast reviews he makes for so many IEMs: http://www.head-fi.org/t/478568/multi-iem-...-08-21-14-p-958

Feel free to ask him as he's quite helpful

audition it yourself is the best 

Understand where you are coming from. But I guess what you need, is not only a bassy warm tone IEM, you need also an IEM with good quality of bass that clearly present the details of the lower mids and bass. can give KC06A a try though.
https://forum.lowyat.net/topic/3335753