Great writeup. I appreciate your ongoing comparisons a great deal. Interesting to see that your excitement has also waned on the Clears.
It may be that the Focal drivers, for whatever reason (say, their metal construction as opposed to the usual plastic drivers), sound artificial and sterile to you, no matter what the chain or components involved. On the other hand, while easy to drive, Focals are extremely revealing of upstream gear and thus require careful attention to synergy. While there exist several sources, such as Dave or Hugo 2, which pair well with all of the Focals (on report), it is not the case all amps/DACs will pair equally with both, on the same level of synergy. The Clear's lower impedance and higher bass hump (relative to Utopia) make them more sensitive to some amps that pair really with the Utopia's higher impedance. With the GSX-MKII, you don't have this problem at all; it ideally works amazingly for driving any headphone. But it is possible its tonal synergy is not doing the "cold" and unmusical timbre you are finding in the headphones through that amp any favors.
I really respect items in your chain a great deal and frankly wish I owned both your main amp and your DAC. As we all know, a headphone really should not be evaluated by itself, especially one like the Utopia. It comes as a package with amp/DAC. Many people with warmer setups than yours have made similar criticisms, to be fair. In this case, the GSX-MKII perhaps is allowing you to hear the headphone most transparently. On the other hand, that kind of pairing is likely not going add warmth to the Utopia one bit and would not be my first pick if I was considering building a system around the Utopia. I would think you'd need to be even more particular about perfect masterings than is already the case with the Utopia itself. I would think GSX would be perfect for an LCD-4/HEK rig, not so much the Utopia for long-term. But admittedly I am just going off written impressions and haven't heard the pairing myself! Your description of it being cold and lacking in musicality from that amazing amp does not surprise me. Maybe try one of those other headphones TBH and stick with your amp.
TLDR: you might never like the Focal sound regardless. SR-009 is already an amazing headphone. But with headphones like Utopia (or for that matter SR-009), account should be given to amp pairings (or DACs and, for some, cables). Maybe that pairing is not synergizing according to your preferences and so it’s best to try another headphone (or stick with SR-009).
I did own the uRendu and actually think that this is likely really helping out in synergy in your setup. I still miss what the uRendu did with the Utopias. It was awesome. Very fluid and slightly laid back, yet beautiful and detailed source. It did impart its own character. Not as transparent as a non-USB source, but my Lynx (especially from Yggy) though more detailed and dynamic than the uRendu, can be slightly too bright and detailed through the Utopia, which exposes everything in the chain. I also thought the uRendu was more suitable as source than the Eitr, though the latter is far cheaper (considering the LPS for the uRendu) and arguably more transparent, while imparting less of the characteristic "musical" tonality of the uRendu. It would be nice if you had another amp around, or one that you could borrow, to see. Or do you still own the WA6?
In my chain, for instance, Yggy is not invariably the ideal DAC for something like Utopia for me with my sources, being more palatable with the uRendu. From what I heard from the Holo when I borrowed it, this was a better match, even though the Holo has excellent technicalities. If the Yggy (which is an amazing DAC) is slightly forward, in your face, 100% on full-engagement all the time, barring you from sleep, demanding attention, etc., this is actually how I would describe the Utopia too. Together, a transparently sourced—via AES input—Yggy and Utopia can amount to "too much of a good thing." I purchased a vintage Sonic Frontiers SFD-MKII, and this DAC for instance synergizes better for all kinds of music, while the Yggy is better for classical and live recordings and, assuming the masterings are well done, sounds sublime through the Utopia, which reveals everything. Like the Holo, the SFD (using a tube output stage) throws a larger head stage through the Utopias, which have been accused of having a small (though deeply layered and precise) stage. The softer, rounder, spacious, and slightly sweet timbre imparted by the nevertheless formidably resolving Frontiers DAC plays so nicely with the sharply defined, dynamic, forward, and nimble presentation of the Utopia. A similar idea is at work with my amp, to be frank. I really would like to hear the GSX with my Frontiers DAC now.