I played with high voltage vacuum tubes for my Hi-fi system a long time ago before transistor amplifiers were available. The vacuum tubes wore out in one or two months and needed replacement for low distortion. The vacuum tubes amplifier provided no damping of the resonances of the speakers due to the output transformer. The output transformers were not good.
Are you using a car ignition coil to drive your plazma tweeters? It is not made for hi-fi audio.
People with tin ears don't use a tweeter because they do not care about how music sounds. The plazma speaker is a high frequency tweeter. If a car ignition coil is used then it will sound like a distorted whistle.