I really like Esoteric K1X performance and also N-01XD which shares the same PCB design with some parts changed. However, both uses MUSES03 JFET single opamp.
I like JFET design but sound signature of MUSES products I've heard aren't really my cup of tea. I'm having thoughts about replacing MUSES03 with OPA627 or AD744.
I used to modify my own and my friends' highend DACs with good results (with appropriate parts not OPA627) since we can't expect manufacturers to maintain studio sound reference given how audiophiles' preferences changed a lot since then.
But I also have a second thought about modding device and if some unrelated issues with device comes up in near future, it may not be a brightest idea to void $40k CD player's warranty.
I won't need to worry about modding used highend gears and I also modded some first hand gears myself. But modding $40k is quite high hurdle compared to $10-20k projects I did before.