Up to 12khz-ish, the Aurisonics ASG-1 is similar; the problem with that IEM is that the response begins to drop off after 12khz, then disappears after 16khz. M HD600 sounds too bright by comparison if I switch right after using these. Of course, take into account that I'm willing to make that compromise for the fit of the shell* and how easy they are to drive using only a smartphone.**
The IE8 on the tightest bass setting seems to be a bit closer to the HD600/650 by my ears, but I really hated the fit.
*It's less dependent on the tips to stay in place, so I can wear a slightly looser tip if I need to be aware of my surroundings; on better-fitting tips it doesn't require a deep insertion nor a tighter tip, so I don't itch nor sweat as much.
**32ohm impedance, less distortion on the bass likely through the bigger, maybe also better driver, and maybe also the impedance doesn't stress weaker output sources as much; I only need about 1/5th of the volume setting on the S3 with these.
