if you think your speakers are bright...........
........if you have what you call bright speakers........the problem isn't the speaker or amp or preamp.........if you have above entry audio equipment it should sound smooth clean and powerful.........not harsh or grainy...........my system includes....rxv995 yamaha receiver....paradigm monitor 9v2......cc350.......titans for rears and ps1000 sub........i had this problem of brightness and what i learned was the power caused it...........impurities in the electricity will come through any quality audio systems.......certain frequences will carry static noise heard through the tweeters........the answer lies in cleaning up the power.........i added a monster power bar and wow! smooth clean and punchy............an earlier post mentioned using resistors to the tweeters which would cut these frequences.........an excellent idea but you might lose some top end.
I find this very difficult to believe
since all power going into your electronics gets converted to DC and any noisy frequency components that would audably effect your sound would have been filtered out by the power supplies of your components.
Ihope you didn't spend a fortune on that power bar
Sorry, there ARE bright speakers.
Some prefer these to others. Some don't. Period...