how bout an A/C unit with a built in dehumidifier? you'll have to have a burp room or the outside to exhaust to, but it will work... I wouldn't use a desiccant because though it would take some water out of the air, it would "use up" pretty quick and it would become more of a hassle than it's worth.
by "Large DWC setup" what do you mean? how large is large?
What's wrong with 60% humidity?
Vapor Pressure Deficit.. humidity vs air temps:
http://urbangardenmagazine.com/2010/07/plantworks-part-1-humidity-and-vapor-pressure-deficit/
Larger Dehumidifier.. running only when lights are off.