I'm on the fence, in terms of the issues (as you'll no doubt have seen, from my posts around 12 hours ago)
At the beginning of the year, I was slightly keener on the Calyx-M, but then they persisted with that stupid, stupid, stupid magnetic volume slider, and stealthily increased the weight from 160g to 230g, which is almost as heavy as an HM-901/DX100.
I want to see the DX90 overcome the teething issues, and then I'll more than likely go ahead and buy one. I can't think of anything else on the market that matches the SQ at $419 and a mere 140 grams.
All good points but with iBasso, considering my experience with my DX50, it's always been a difficult thing to get right, it took quite a few months to move to 1.2.8 and it is still not fully functional, so my feelings is that you'll never reach this so called status of done. I understand your quest for less expensive and SQ improvement but with all ventures, something's gotta give (there is nothing like a free lunch, sooner or later you'll pay, spending lots of time fiddling around with the player is money lost doing something else cause time is money lol). The pool of resources at iBasso is limited and you'll never reach the level of a Sony and Apple on the front. With the DX50 and DX90 unfortunately it will never be done so the best time to join is now and participate in the journey of improving it months at a time.