No complaints here. As you've mentioned, run in helps a lot in these regards. It certainly works well with the JHs.
Bluebear, it's a minor point in the grand scheme but the DX90 may be phase inverting. Just a guess from listening. Try flipping the pin end of your 1p2 cables and see if you get more depth etc. I say it's not a big deal because a good # of amps, IEMs and recordings are inverted as well.
Interesting. I will try it again and flip the pins around and see how it sounds. Will also put it on high gain and just turn down the volume like what you have suggested.
Well everyone has different taste when it comes to audio preference so it may be hard to define what is better/bigger soundstage and our favorite collection of songs may also be from different genre. But I can say at least for myself I define a bigger soundstage to my music as one that sounds like I am listening in a big "live" concert hall type of venue or at least in a big ballroom environment. Bigger may also not automatically imply it is better, so the music quality must still retain its accuracy and clarity even though everything is now placed further out from you in a larger environment. I can still pinpoint the individual sounds from those accompanying instruments in the background with ease. Their relative volume amplitude should also not be diminished compared to the foreground music, i.e. if their volume is at 20% of the foreground music then it should remain at ~20% even after spacing out into a bigger environment in a good DAP. Everything should scale up accordingly without distortion. Of course, separation of instruments comes hand-in-hand with soundstage. It should also be good and well taken care of and not sound like everything is sounding from the same spot in the 3d space. So to answer the question of how big really is considered better, IMO I would say as big as it can until it reaches the optimal threshold where the quality starts to give way to distortion and affect the SQ and separation. In other words, I am pushing the limits of an IEM to get it to sound like a real speakers in an open environment. Not some narrow closed up reproduction of the music which can still be accurate but does not come close to speakers style signature.
So if you ask me, I find my initial impression of DX90 to sound less "wide" and nearer to the listener because the individual instruments and the mid vocals all sounded like they are in the same flat 2d plane, i.e. they sounded just as loud and I detected less separation between the lows/mids/highs in their virtual "placement" in the soundstage. Could be a lack of burn-in issue which I will check back on the DX90 again once it has enough time to burn in as well as the phase inverting problem that goodvibes has mentioned. It could also be the side-effect of being more reference in characteristic and making everything flat, but then AK240 is rather neutral and flat compared to AK120, and yet it can still sound surprisingly musical with a very good soundstage/separation.
If you feel pairing Roxanne with DX90 is already hitting the limit of what wide soundstage is like to you, then I am very sure we have different taste to our music. IMO Roxanne has a rather thick/veiled SQ making the music sound very close to you and intimate, a.k.a. warm and I also find the details in the highs lacking. That is my impression even after turning the dial all the way down to minimum to kill the bass. Maybe a better analogy of a wide soundstage with airy feel that I am more comfortable with would be the HD800 signature. You probably prefer the TH900 kind of narrower soundstage with more warm. That is not saying TH900 type of signature is bad. It is just different to cater to a different group of music listeners. For example, tyeck reported the same impression on his Roxanne. Could be possible his preference is more like mine than yours. IMO I just find that a thicker/warmer sound signature always give me a feeling of suffocation/intoxication and makes me always crave for "air" and details like I am dying of thirst in a desert. Just trying to paint a visual image for you to understand my point of view.
One of my favorite test tracks for high-end response is Pink Floyd's Happiest Days of Our Lives (The Wall). There is a 16th time hi-hat cymbal in that track starting at about 0.39. On all 3 my main audio systems (high-end, home theater and desktop) as well as my HD650 and also from memory, my UE 10 Pro, that cymbal is fairly prominent. On the Roxannes it is not prominent at all. The first few 5 beat salvos are there but veiled. After that, the constant cymbal is very indistinct. If I did not listen for it I would almost not notice it. Even the vocals sound like they are behind The Wall :). So for me it is not that the Roxannes are merely laid-back vs. my personal preferences. I feel the Roxannes are completely almost hiding some detail.
Would you possibly be able to do a comparison of that track on your different headphones etc. and let me know your impressions? If you hear it distinctly and prominently and consider them as detailed as your HD 800 then I will have some hope and will explore with you further about DAP/Dac/Amp pairings etc. and hold out for burn in. Thanks again.