You could explore different output transformers. There are many that I would consider a downgrade from what we provide. I believe you could ask Sowter for a custom unit and I would specify a full nickel stack since power handling wouldn't be an issue. On the downside, maintaining the impedance and balance switching with an aftermarket transformer would be a total pain. I'm sure it's doable, but I'm not sure I'd want to have to figure out how. Their tiny mu metal headphone output transformer is a little on the small side, but the big gapped stuff is a little on the big side. You'd want something in the "D" size. It would end up being over $500 USD I'm sure for the pair, and I wouldn't be certain that there would be a giant difference in performance.
You could perform serious surgery and use the 8608 instead of the 6C45P. Again, nobody will really know if it's any better or worse until someone tries it.
That's my long list of strange ideas. None of them are sufficiently compelling for me to spend much time on them.