Most dome tweeters have the same problem in that the top of the dome resonates at the upper end of the audio band that can add an edginess or sizzlly quality to the highs. You will notice that your tweeters have a lens covering the dome of the tweet. Usually these lens's are put in place to block as much of this extra resonate energy as possible.
If you want to try an experiment you should pick up some felt dots that are sticky on one side and try putting them on the tweeter lens. Start with one about the same size as the lens and work up from there. The idea is to increase the effectiveness of the lens without negatively affecting the tonal balance. The dots are easily removable if you do not like the effect or when you are ready to sell the speakers.
BTW you did not mention what other sources sound like? Do you have a CD or DVD hooked up to the system?
If you want to try an experiment you should pick up some felt dots that are sticky on one side and try putting them on the tweeter lens. Start with one about the same size as the lens and work up from there. The idea is to increase the effectiveness of the lens without negatively affecting the tonal balance. The dots are easily removable if you do not like the effect or when you are ready to sell the speakers.
BTW you did not mention what other sources sound like? Do you have a CD or DVD hooked up to the system?