Andrew,
It sounds like the Orpheus is breaking in nicely. The fact that it now sounds better at a more normal 100 ohms than at 47K is consistent with that. I've had new MC's that sounded okay at higher impedances OOTB, but needed progressively lower impedances as I put hours on them until they finally reached happiness at the expected setting.
I wish we'd had more hours to play with arm height during your visit. Your results make sense. Our cartridge also sounds muddy and less micro-dynamic when SRA is too low. Glad to hear working at this is paying off so well. I'd love to hear it again some time, optimized in your system for instance!
All the best,
Doug