i have re600 for less than a week , yet i sense where its sound signature lies
first of all these don't need an amp, as they sound even louder than the 272 (the 262 need an amp due to their big impedance)
compared to the 272 (which was the previous iem flagship for hifiman and my favourite iem ever) it is more mid-centric(like 262) but also more forward.
the mids are more warm and thick but the detail retrieval is very good, even better than the 272 (mid-wise only, in the highs 272 is unbeatable)
the bass also is very robust and full compared to the anemic bass of the 272, where i always use 272 with the bass boost of arrow 4G on, with 600 i turn the bass boost off
the highs are not as good as those in 272 , but then again nothing touches the perfection in the highs by 272
272 and 600 are very different iems , even more so than when comparing 262/272 (i always thought that the 262 amped sounded quite like an unamped 272)
i have a feeling that the 600 is still changing soundwise due to initial burn-in, so i will return with impressions
i like what i am hearing so far though and it is a completely different signature/approach from the 272