I was going to wait for a responce to the 'binding post straps' suggestion, but what the heck..
I'm betting it's the straps, or something to do with the way the system has been set up.. Cross phase wiring, bad or faulty connection, etc ?
Now, to address the brightness issue.. If, after all this, you still find them overly bright, just give it time.. It's been said before, but again, it does take time to adjust to a new set of speakers.. Not that 'they' need to be broken in, but that 'your ears' do.. Like a new pair of sneakers, they never really feel right at first.. You compair them to your favorite beat up old pair, and think the new one are too tight, or they pinch, etc.. Next thing ya know, the new ones are broken in, and in no time they are the only ones you wear.. Same same with a new car, new job, etc..
Bottom line, get those Sixties hooked up right, to a working power source, and get yourself broken in..
