Thanks, guys. That makes a lot of sense about the lack of frequencies. As I recall, the wireless speaker concept was coming into vogue about 10 years ago......just when the mobile phone boom started.
And as Fran said, it can be done, but I'm guessing there would be a lot of dropout especially at those distances.
I'll survive without it for now, but it would be nice to have a pair of 12's in the back of the room to fill out the sound.