I think I heard a pair way back in 1978 at the local stereo store. I got a pair of HPM 40s before heading to college. powered them with a Pioneer sx450. A kid in my dorm had 60s and an sx1250. I was a bit envious. Eventually gave then to my dad. They are still in what was his house. The foam surrounds rotted years ago. Now I am tempted to retreive them from the evil mother in law and fix them up. I have always wondered how the Gallo tweeter differs from the HPM.
Good luck in your quest.