Seems to me you need more efficient speakers, and really you might want to look into a pair of used PA cabs.
BTW if you think amplifiers waste energy you might be really disappointed to know that a speaker wastes up to 99% of that energy as heat.
A "PA cab" is what, the cabinet of a public announcement speaker?
I looked it up and all I saw was taxi cabs. (You shoulda seen me learning how to use computers. It was a mess.)