Welcome!
I use s/h for my cattleyas with great success.
I personally have not had good success using s/h for my oncidiums. I use Aussie Gold for them which I don't know alot of people that use this.
Good luck with it though
The dendrobiums I don't grow but my hubby has a few. He was willing to let them out until the weather was 40's but I went out and brought them in
We are arguing over it a bit still
They do need to get cold though.
Soft water is probably more of an issue with your Oncidiums than humidity. Try distilled water from the super market and fertilize sparingly.