Brassidium Dragon's Flight 'puff' culture question

[Rocinante]

I purchased this beautiful bloomer earlier this summer. It had a great fragrance and a beautiful spike. But now that the bloom is recently finished, I want to re-pot. Without having actually pulled the plant out of the pot, it appears to be potted in volcanic rock. I would like to re-pot in the same medium it is accustomed to, but I can't find volcanic rock for purchase. Judging from the roots growing wildly out of the pot, it seems to have a fine root system. I have sphagnum moss, different grades of bark, coir, and I just bought some Aliflor; which I am tempted to use.
Opinions, please?