I think I would go with sphagnum moss because it holds more water, similar to the peat mix that your plant is currently in. I once moved a Den. kingianum keiki (with multiple pseudobulbs) from pure sphagnum, where it was thriving alongside the mother plant, into its own pot with bark. It died within 2 weeks. Obviously cultural issues likely also had a role, but I would say play on the safe side and use a medium that is similar to the previous one. That being said, nobile-types are
tough. And you have lots of backups.