I may well change my amp for these speakers. I am using SS amps with them is this is likely part of the problem. I was using some Heathkit 4W-AM push/pull 20w monoblocks... but the sound was very bloated and unclear... much worse than the SS amps, perhaps the tubes... I'm not sure. I will likly sell the Heathkit amps and look for some Bottlehead or Decware tube amplicication.
I will also attempt to treat the piezoelectric horn as you have stated and check to try to find the website that can tell me more about altering the inside of the horn...
Thank to all..