For the STAX X9000, I had a little doubt about it seating property around my ears given the loose fit. But very, I mean very technically capable headphones.

I listened to them again today! I will say this. For bass, go with the ZMF no doubt. The Caldera is perhaps the most technically capable one from all the ZMF I heard these two days, but it retains their sound signature. I personally liked the Verite a lot. The 009s is faster and more slightly more detailed to my ears (the sound reproduction just sounds effortless). Given the issues you described, I think the Caldera can complement well.

I’d agree that the intimate vocal presentation of the Caldera is better, and I will need to spend more time with STAX to familiarize myself with estats. It was indeed my first time hearing it, so I think the wow factor did play a role. I will report back if I have more impressions and comment more on these issues.