To much high

"To much high"

Is that different than 'From much high'?

I think you meant 'too'. :-)
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I would have to say that the statement of 'wasting time switching cables' is a little off the mark, as cables can greatly impact the overall sound. (Van den Hul vs. Kimber, in general, have totally contrasting characteristics - Van den Hul being warmer/slower vs. Kimber being lively and quick). Having said that, I believe a combination of what was stated in the previous responses can help to finely tune / tone down the 'brightness'. Try placing a large area rug on the floor in front of your speakers. Also, putting some form of sound absorption material on the wall behind this system will greatly help, whether it be a wall-hanging decorative rug or sound absorption material specifically designed for that purpose. Side walls (first reflection point) and wall behind the listening area should be similarly tamed. Some or all of these changes can help to tame the beast and won't break the bank in doing so.

I definitely agree with NOT using errors in other components to fix errors in another.

Try to fix your room as much as possible. After that, add a resistor to the tweeter circuit. (This resistor must be added BEFORE the tweeter's filter cap or you'll change the crossover point. This may be easy or difficult depending on the complexity of the crossover.)
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I agree that treating the room is definitely the best approach. I will not repeat any of the excellent advice already given.

However, if that is impossible, for either room constraints or spouse constraints (Boy, I know the later!), than rather than switching speaker cables, perhaps you could try something less expensive like switching out the interconnect between your source and preamp, or between your preamp and amp.
You might want to try a Cardas Golden Cross cable. It might just take the edge off the brightness. (A friend of mine used to use these cables to take the edge off his CD player.) You should easily be able to find a used pair on Audiogon (or Ebay) and give it a shot. If it does not work, you can easily get most of your money back. (You might want to ask any friends who are audiophiles to lend you some of their cables, so you can experiment. I have lent out cables for that purpose before.)

Just a thought. Good Luck!

Definitely treat the room. And, as has been suggested, going to a different IC can often help with the shrill highs. Although I prefer silver cables with our tube-based system, I found the Audience AU24 IC and the Analysis Plus Crystal Oval both took some of the high end edge out that is present with the silver IC's. There are many excellent options out there.
Hope this helps.