Miltassia Dark Star 'Darth Vader' help please

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In Oct. my friend gave me a fairly large plant of Miltassia Dark Star 'Darth Vader'. It was nice and healthy looking and she had just split up a huge plant and potted the pieces in SH. Not knowing what really to do with SH (It was in all leica balls) I set it in a shallow pan and put it under the lights with some other potted orchids. The shallow pan had a bit of water in it at all times. But within a few weeks and until now, I kept seeing the odd leaf turn yellow and I was concerned about rotting the roots. It is kept in the greenhouse. That area gets to about 67 or 70 in the day and down about 10 degrees at night. Lights are on for 12 hours. I just un-potted the whole plant today and I I think most of the roots are dead. They are not mushy, but brown and rather firm. I don't have a lot of experience with oncidium types but I thought the roots would be a lighter colour. I pulled some away and some of the old bract leaves beside the bulbs are mushy and I tried to clean all that up. I cut it in two pieces and a 3rd small piece just fell off. There are new growths on all 3 pieces but not many new roots with the new growths. Orchid Wiz says common potting media is bark. It doesn't say small or medium. The roots are very fine. I have very fine bark for some of my Paphs and medium bark that is about 1/2 to 1 inch in size. I also have sphagnum moss.

I would appreciate any ideas as to how to proceed with potting these. I am tempted to soak them for a few hours in water treated with KLN rooting hormone, but do I dare give them any more water in large amounts? And then what do people use to pot these plants for good success? Any tips would be appreciated. I will hold off and hope for some responses.