The run in (break in) is your ears not the speakers. The mids are crossed over to the tweeters at 2 KHz so they will not contribute to brightness.

If room treatments are not an option, does your avr have tone controls or EQ? you could try taking a little off the trebble to see if that sounds better to you.

Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!