You have quite a number of options for reducing the high frequency output. Here are a few ideas. Easiest is to use an equalizer instead of a tone contol. This gives you more precise and flexible control. Next easiest is to add an addition piece of grill cloth or two in front of the tweeter. If you are handy with a screw driver and soldering iron, you have some more choices. You can wire a resistor in series with the tweeter. This will reduce the overall tweeter output. An 8 ohm resistor (I'd say about 5 or 10 watts would be ok) will reduce it by 3 db. You could add an 8 ohm L-pad to the tweeter for a continuous level control. You can "equalize" the tweeter also by adding a series inductor and/or a shunt capacitor to the tweeter. The values will determine the rolloff frequency and by using one or both, you will get either 6 or 12 db fall per octave. I'd try a pair that added a rolloff at about 14 khz to start and work down from there. Formulas for calculating suitable values are available many places such as Parts Express website and the parts should not be too eqpensive. You could also substitute a different tweeter or bi-amplifiy (not bi-wire) the speaker so that the tweeter has its own amplifier with its own gain control. If I were to choose, I'd go with the equalizer. It makes the most sense to me.