Repot, or not? Medium for Cattleya dowiana and Trichocentrum splendidum
 

I went to my local OS meeting on Sunday, came home with 4 plants:

Neolauchea pulchella (= Isabelia pulchella), mounted on cork - freebie!
Epidendrum radicans (blooming - freebie!)
Cattleya dowiana
Trichocentrum splendidum (formerly Oncidium splendidum, a mule-ear type)

My question is about the last two. The plants are both quite young, the C. dowiana has pseudobulbs up to 1.5 inches tall, leaves up to 4 or 5 inches long. The T. splendidum's longest leaf is about 3 inches. Both came from a vendor I know and respect, and the plants appear to be in great shape, good roots, and each has a new growth that is about half-mature (elongated but still flat, leaf not open, no roots emerging from the new growth).

So here is my question. Both of these plants are currently potted in sphagnum. And growing well in sphagnum! This vendor grows just about everything in sphagnum (greenhouse, of course, where moisture can be managed). The vendor advises that I keep growing these plants in the sphagnum. But, everything I have ever read about both of these plants is to grow them in medium that is very open and fast-draining. Decades ago, I has a T. splendidum that eventually succumbed to root rot and soft brown rot (I watered too often, most likely). I grow outdoors April through October, weather permitting, so plants can be exposed to prolonged rain (or prolonged dry, and heat). Indoors under lights the rest of the year.

My "gut" reaction is to re-pot into a coarser fast-draining material when roots start appearing on the new growths. I'm thinking of either planting in scoria (= lava rock), or a combination of cork chunks and charcoal. I am open to other suggestions, though. The pot would be either a terracotta pot, or a net pot set into another pot.

Any thoughts or suggestions?

I grow my dowiana in a coarse bark mix. I feel that a mix wit clay pellets, Perlite and pumice works better than pure bark. I have no good experience with sphagnum over a long run, and it is difficult to manage if some plants grow in sphagnum and others in bark.
For dowiana a nearly dry warm rest period in bright light over the winter is essential to stay healthy.