No headphone not hooked up to a Smyth A16 Realiser has a soundstage
I can understand this and support the critique when comparing headphones to speakers, it's a whole different game. But when I consider soundstage I refer to something more close to "headstage" rather than a frontal stage set up in front of me. In this instance, critiquing "soundstage" in headphones seems forced and inappropriate, as I clearly perceive differences between iems and, most importantly, headphones. In other words, just because it has no frontal stage doesn't mean it doesn't stage and separate sounds at all.
As you said, fitment plays a huge rule in this, but also your own hrtf. My own critique against headstaging as stated by reviewers is when they try to universalize their own perceptions: it's not the iem that has an inherent big stage, it's that iems curve's interaction with your specific htrf (given, there are more big stage FR than there are others). Another factor that may influence that is the openness of the design.
For me personally, most if not my all iems image perfectly, most likely due to the fact that I like pronounced pinna compensation AND that iems seem to have lesser problems with channel matching than headphones. Still, there are ones that stage bigger than others: my zero2 and b3 eqd to harmanish are intimate and close sounding regarding space, whereas the timeless AE and MD ssr stage almost out of my head, most likely due to insertion depth.
Android phone and USB Audio Player Pro with the added professional tools by Tone Boosters which cost around $10.
I already do, but I prefer doing it with autoEQ or squig prediction then export it to wavelet or peace. It certainly is a neat feature and tool, just be careful not to take the FR differences for granted: as you said, fitment plays a huge role, and given that designs are complex, EQ won't always behave analogically as you expect them to do. As I said, it's very hard bypassing the upper treble swings/reflections/résonances of single DDs. Inversely, some designs like the dusk and b3 use a damper in the bass tube, so a dB changed in EQ most likely won't result in a dB changed in SPL. With this in mind, the only way to make sure the EQ is set properly is to remeasure the FR with a coupler AFTER applying the filters. Oratory is the only one that does this consistently, and crinacle probably went this route when developing and testing the dsp profiles, but you can go down the rabbit hole and buy a coupler yourself, which is something that haunts me from time to time
