|Classical requires some awesome bass, if you've ever been in front of a full orchestra. The timpanis resound, not only on impact but on sustain. They blast and then continue booming. The double bass also resounds, with some passages requiring that the player strike the bow heavily, causing a very visceral sound. With a cymbal crash comes the loud boom of the bass drum under it.|
IE8 are most impressive with orchestra, but bass is too much and needs an EQ. HJE900 are good too if you foam mod them to dampen the highs a bit. FX500 have fantastic dynamics and bass but the highs are quite harsh. RE0 are a common recommendation but considered bass light. I'll get a loaner pair next week, so I can't say anything more for now.
Last but not least my favorite IEMs for classical are the budget Playaz N1, extremely open and airy with vast soundstage, but they suffer from driver crackling (not suitable on the move) and need heavy EQing that you can only do with Rockbox or a Cowon IME.