Soren Brix in Denmark and Dukei (Miroslav) are also reputable builders, you can either get a Carbon or a Grounded Grid, they are more or less similar, one is all-solid state, the latter is a hybrid, mostly solid-state with 6CA7 tube output.
I would also ditch the X9000 for a 007, as in my experience, the X9000 still sounded anemic on the KGSSHV.
The amp makes a big difference, but it's not going to fundamentally change the character you are hearing from the headphones. You can also read more and see, that it's not a universally-loved headphone just because it's the most expensive.
I've gone back to listening to the modded 727 with the 007 Mk1.
Yes, I really miss the control, precision and dynamics of the KGSSHV so I will intend to sell the 727 at some point, but I would not really call this combination unenjoyable, especially for the price. And the more prominent upper mid, more subdued treble, more diffused staging of the Stax amp seems to have a decent synergy with the headphones.
I definitely don't fancy the softness, lack of dynamics and bass control (this is the most annoying) but I think it is partly due to headphone itself (as I read it as still a little loose on the Carbon), but it's still the same character that is full, unoffensive and quite enjoyable.
Bending the arc assembly and fixing the headpad made just as much difference as the amp.