I just signed up for a free course from Coursera called Introduction to Digital Sound Design from Emory University. Coursera is a site offering free classes from universities around the world. The Introduction to Digital Sound Design course offers a certificate at the end.
There aren’t a ton of classes of interest to the field of stagecraft, but there might be other things you might be interested in. Digital audio is going to have more impact on sound people as more digital audio desks go out, and people start running fiber and digital lines from backstage to FOH. Get on board now.
You can find the digital audio course here.