I listened to your track and the sm3 had no problems keeping up and there was no congestion, though the jvc's displayed greater dynamics over the sm3 in that passage.
I would think something with this frequency response could sound pretty congested at times, no? That appears to be a lot of mid bass overshadowing the lower midrange.
Edit: This is a genuine question (not meant to sound smart). This is one of the reasons I never tried the IE8. Just trying to understand where you are coming from.
I appreciate you taking time to experiment (tho' I almost hate to display gratitude in that it is psychological friction and our strong-headedness that keeps things interesting and, more important, technological evolution moving fwd!). Bottom line: I wish you folks wouldn't beat me up a bit more! IAC ...
I'm not surprised you did not hear the diffs. with that Mahler segment. "Audiophile" differences are often subtle and/or require some familiarity with the program material. Choose a passage from a track YOU are most familiar with; that passage should be complex with heavy transients (lots of instruments/voices/action-movie-segment and/or multi-track layers, in high relief, and rapidly-shifting loudness for each instr./voice/effect/etc.). Dealing this type of signal, the SM3s under-perform compared to my IE8s and SE530s. Given the various and multiple write-ups describing its characteristic sonics, I'm not surprised about the JVC FX700's superior dynamics.
The freq. response has almost nothing to do with congestion. Yes, I do think the IE8 sounds flatter -- and flatter in a better + important (= more linear) way -- than any other IEM (and many full-sized + high-end cans) I have thus far heard. SM3s have a mid-range "hump" but extend more into lows and highs than my SE530s (which I often call "all-mids" [similarly, Stax electrostatics, especially older models, are "all-treble"]). Speaking of treble, the SM3s have a harder/grainer/duller treble compared to the IE8s (which are more extended and delicate and refined).
Overall, anyone contemplating buying (or upgrading) to the SM3s should, perhaps, save their pennies a few more weeks, and opt for ... say Sony EX1000s ...