I use the IE800 with the DX90, and also with the AK100. They sound great on both. On the DX90, the overall SQ is more open and dynamic. The AK100 sounds good, but a "dull" sound in comparison to the DX90. Bottom line, the DX90 plays music that is more enjoyable.
This is only my subjective impression about the IE800, as I don't have the range of equipment that other people have to compare with. Or have done the same rigourous comparisons.
I did have the Westone UM1, UM2, and the UE TF10. I had the TF10 paired with an RS P-51 headphone amp. Still have the TF10, and did a quick comparison with the TF10 when I got the IE800. The IE800 makes music much more enjoyable.
I've also come to a conclusion that I prefer dynamic drivers over BA, after previous experiences with cheap Nuforce dynamic earphones, which I found I enjoyed the way they produced music more than the BAs that I had tried. I hasten to add that this is only my subjective preference within my own experiences, and I have not tried some of the highly rated multiple BA or BA/Dynamic combos, so my preference is not a judgement on them.
So the IE800, being a single dynamic driver did not put me off, when comparing against multiple BA drivers. I also theorize that a single driver, done well, has advantages due to less complexity with complex crossovers, multiple drivers sound interaction. Multiple sound sources, time delay, cancellation, differences in efficiency, etc., etc. For loudspeakers, very clean single, or simpler point sources have a purity of sound that stands out. i.e. It is much harder to engineer a multi (3-4) driver loudspeaker, than a simpler two way driver. And very simple crossovers have less of an interaction with the sound. Less is more. So the same rules should apply to earphones. The greater the complexity, the more you are putting in the path of the signal.
Of course, creating an "excellent" single dynamic driver earphone, which is a very simple point source, compared to 3-8 BA or combination BA/Dynamic drivers, is no small feat. But if Sennheiser has done it properly, then this gives a choice of a good single driver point source, versus multiple driver implementations. Another choice, in a different design direction. There is of course no absolute in any of this. Just look at what goes on in the loudspeaker arena. Very strongs opinions by respected people with opposing preferences. The same in Amplifiers, DACs, etc.
So, I do enjoy the music out of the IE800, and think it is a good sounding earphone. I don't regret the money spent on the IE800, as I enjoy the music through them, which is saying a lot, as it can very easily go the other way.
And I do not look at the single driver as being a reason to ask: "why are they charging such a ridiculous price for a simple single driver headphone?". I think of it rather as "damn, Senheisser really did a great job engineering a single driver to be this good". A comparison can be made with Kondo's (Audio Note) hand wired SE amplifiers. How can something this simple be this expensive.....
