Yes, I've found my holy grail. Well, it's on its way. The Etymotic ER4SR. I friend traded me an Etymotic HF5 for a Shure SE215. This little single balanced armature has left me in awe. I've had the opportunity to compare it HD600, HD540, HD800, and Focal Utopia. In some ways it is a bit in between the HD600 and HD540. It has some of the HD600 weight. Both 540 and 600 have an incredible natural mid-range and the Etymotic follows suit. The HF5, on binaural tracks, sounds almost completely realistic. I've listened to nature recordings, where for the first time, I felt completely encapsulated with the HF5, completely immersed in a 3D soundfield. Detail is incredible with the HF5. I've read the term microdetail banded around, and I will say the HF5 has that in spades. The HD540 is overall a bit more (macro)dynamic in the sense that it appears to have a larger headroom, in larger part to being an open back dynamic driver. My HD800 also sounds more immense in the macrodynamic respect, but the HF5 can still be huge, it just seems to be a bit more compressed in overall dynamics. This may just be a psychoacoustic effect though of listening to IEMs vs over-ear. Still, I would be very very happy having the HF5 as a daily driver. At the price they go for used or new old-stock (including the HF3 model) it is one of the best values for reference sound - not just for IEMs, but for headphones and speakers of any kind. Take a look at the graphs on Golden Ears, you will see that both HF5 and HD540 have near identical signatures, and come close (aside from the sub bass) to matching Golden Ears diffuse-field reference target - which makes sense given that Sennheiser and Etymotic are pioneers of DF. HD540 http://en.goldenears.net/16553 Etymotic ER4S (an older model to the new SR but very similar in presentation) http://en.goldenears.net/1512 The HF5 confirmed that the diffuse-field clicks with me. Classical, ambient, jazz, electronic, and especially for binaural. I laugh looking at the Rtings review of the HF5, as it couldn't be further from the truth. The new Harman curve that some people are measuring against, seems to be one of popular opinion - but that doesn't make it necessarily the right curve. Just averaging people preference for sound doesn't mean you are getting accurate sound. I've played the HD540 for some and the response I get back is "where is the bass". This is a common thread among Etymotic ER4 discussion as well. Some fans are ardent supporters of the original tuning that is decades old, while others want more bass. Even the Golden Ears target will show that both the 540 and ER4 roll off. I'll say, once you get used to the sound, even the amount of bass seems right. Sure it won't give you a tactile or visceral impact that might simulate how you feel bass performance, but for a lot of listening it is accurate in what bass is heard. Generally, classical, jazz, soul, funk, acoustic, all will sound stellar on 540 and HF5. More thumping modern pop type music, perhaps less so. I enjoy bassier headphones as well, so I hold my final opinion. Perhaps if I heard a headphone that could nail the response curve of the ER4 and add bass - I might just deem that the best headphone in the world. Actually, there is one that comes very very very close to being said headphone and that is the Focal Utopia. The 540 actually had a bit more air than the Utopia which seemed better for classical reference recordings. The HF5 really does deliver though. Within a month of ownership, I purchased the ER4SR. I'm enjoy the HF5 so much, i'm almost a bit scared that the ER4SR won't be as good... but I think I'm going to be pleasantly surprised. It has actually ruined things - in a good way - even more so than the HD540 did. Both are low cost. Both are so musical. I've considered pairing my setup down to HD540 for open / convenience, ER4SR for true accuracy, and XBA-Z5 (or 7550) for bass / sumptuous tonality. But as such, I'm inundated by cool and unusual headphones. If you go the Etymotic route, be sure to check out the thread. Give them time, make sure you properly insert them, they will get more comfortable over time. Also, the HF5 is an old model, still worth tracking down, but a more up-to-date model is available in the ER3SE. Really, Etymotic is committed to this sound. I would avoid the ER3XR as it is tilted down in the high-frequencies as tilted up in the lower range. The ER4XR has the same curve as the ER4SR but elevated bass that may bleed into the mids a bit. The ER4XR may be perfect, but I really want to hear the ER4 signature first. ER4P is closer to the HF5 signature, and a bit warmer overall. Anyhow, listening to them now. Took me over a decade to finally get into Etymotic, and what I had read was true all these years and will likely remain so.