Is this medium ok for my orchids?

[scy]

When I got my first orchid, I had to do an emergency repot and wound up buying a bark mix at my local Lowe's. They only had 1 selection with a bark mix and consists of medium fir bark chips, hardwood charcoal and coarse perlite. It's a large bag, so I'd hate to waste it. The only other medium I have is PrimeAgra, which I used for transferring my dendrobium to S/H.

I wanted to know if I can use the bark mix for my cymbidium and miltoniopsis when it is time to repot them. Currently they are potted in a terrestrial mix. I checked on RepotMe's website and they use the following:

CYMBIDIUM MIX: Small Coconut Husk Chips, Medium Redwood Bark, Coir, Small Stalite, Small Sponge Rock, Rice Hulls

MILTONIOPSIS MIX: Small Coconut Husk Chips, Small Sponge Rock, Small Charcoal, Rice Hulls

I tend to be heavy handed when it comes to watering although I tried to water without drenching it in the winter.

My growing conditions:
- East facing window
- Low humidity
- Varying Temperatures Ranges
- Winter Daytime: 75 - 90 F on sunny days; 60s on cloudy days.
- Winter Nights: 45 - 50s F
- Air movement: The central air vent is above the orchids but is not heavy enough to move any of the leaves.

If I change the medium, will the roots die because they are accustomed to the terrestrial mix? When I repotted my phal from sphag to bark, I noticed that some of the roots shriveled up and turned brown as opposed to the plump roots it had prior. Any suggestions? I'd hate to buy 2 separate mixes since they are in 4 & 5 inch pots. Thank you for your advice!