How to protect the wood finish of speakers.

Only two viable options. Either cover them up as suggested, or invest in ultra-violet sunscreen film for your glass. I've got an 8' x 8' glass patio door by my system and installed sunscreen film. It cuts down on glare, enhances the energy efficiency of the door, and stops 99% of the uv light that damages fabric, wood, and art. Plus, it actually improves the view. It has an effect like wearing polarizing sunglasses, the sky looks much bluer.

One thing an owner needs to consider is the type of finish on wood. Most speakers of modern manufacture are going to be finished in some sort of catalyzed impermeable finish. No amount of beeswax, oil, or whatever is going to have an iotas effect on the wood. It may make the surface look pretty, but it's not going to affect the actual underlying wood unless you have an oil or wax finished veneer. And those are fairly rare these days. Conservators wouldn't trust sunscreen products to protect any valuable wood item. They may help a little, but don't be lulled into a false sense of security and think they'll stop sun bleaching, especially in places like Florida, Arizona, or Hawaii.