If you are cranking the trebble all the way up to get the sound you want there is something wrong. Speakers are designed to be played without the tone controls engaged. They are/were there to make
minor adjustments to match your taste or to make up for room effects.
Even if you don't fry your tweeters, I expect that you are driving the tweeters beyond what they are capable of, introducing all sorts of distortion.
Considergoing to a local electronics store and find some speakers you like the sound of without cranking the trebble. Then, take your speakers to the store and compare them with and without the trebble cranked and see which set you like better.
Long term, it's not good for your ears, either.
Funny you should mention that, because that was one of the things that popped into my head in the 'somethings not right here' category.