Have had the 3xp for a week now; will try it for a bit longer but probably will return it. Overall compared with the A90 (which has been my daily driver for a while), the 3xp presents a warmer tone on the higher frequencies + boosted bass. On some parts, particularly the higher mids and treble, it's a welcoming improvement; however on the low end, even upper bass, the boost is not pleasant on the Diana TC.
So one of the minor issues I have had with the DTC on A90 is that some high-frequency vocals and treble instruments can sound too bright. The 3xp does fix this issue; it has a smoother, more relaxed sound in those regions and is enjoyable. however the 3xp introduces a much greater and persistent issue that doesn't work for me. Basically it boosts the pressure/energy of drums - toms and floor drums. This is probably a welcoming boost for most other headphones, but the DTC has very strong bass already and this boost simply moves all drums forward in all music, even those are aren't really bass heavy. It kind of hurts my ears... basically on the A90 vocal volume is the limiting factor while on the 3xp bass volume becomes the limiting factor - thus vocals sound less prominent, on essentially all songs. Yet since I want to hear the vocals, the bass ends up hurting my ears...
I don't know if the 3xp sound can be achieved with just an eq from the A90... not sure... don't feel the lower bass, particularly electronic stuff is that bad, it's really just drums... feels like drums moved much closer to me... too close... can feel their percussive power going into my eardrums... so not even sure if I can call it a bass boost, more like a percussive energy boost. This is all on power amp mode. Tried the normal mode to begin with, but mids sound too recessed - feels dark sounding and not enjoyable.