Someday I may purchase a systemic fungicide with benomyl as you suggest. I won't lower the humidity in my home because I need it for myself as much as for my orchids, but for the time being I think I am getting the crown rot and root rot under control. I never mist my phals anymore above the roots and therefor never deal with water collecting in the crown. I treat fungally damaged plants by soaking them for 15 minutes in a slightly diluted hydrogen peroxide solution after cleaning the roots and before re-potting. And once I get my worm compost system set up in my house (hasn't arrived yet) I will be fertilizing every other week with the worm tea dilution, both the roots and the crown. Worm tea is said to be very effective at preventing new fungus growth and reinforcing a plant's internal defense system.
Until then I guess I can go ahead and use the Safer brand sulfer spray, since you say it is effective and safe for the orchids. I'm leaning toward avoiding the systemic fungicide for now, what do you think?