Hi Everyone!
I wanted to follow up on this old thread with an update.
By June or so, some 6 months after I first received my Summit Xs, they had broken in nicely. That thin, hard midrange is now gone. The high end is still articulate, but is now very smooth and enjoyable. Many contributors to this thread suggested that my room could be a problem and it is possible that the installation of window shades (which are always down in the "translucent" position) helped with some ringing off the bare glass surfaces. I did note an improvement after the shades went in. At the time I first got the Summits, the amp and preamp were also new, so perhaps those components have also broken in, yielding another positive improvement. Other factors influencing the better sound are using the 2 ohm tap on the McIntosh amplifier and switching to the Transparent speaker cable.
I spoke with Peter Soderberg at RMAF this year and described my initial experience with the Summits which you can read at the top of this thread. He indicated that my experience was completely typical. The owner's manual talks about break-in related to the woofers, but Peter said that the panels go through an equally dramatic break-in process. So I asked him, "Why don't you guys just say in the manual that these speakers are going to sound like absolute crap until they're broken in and to give them 6 months before passing judgement?" Well, apparently, they did have those discussions at ML, but they were concerned that saying something like that would put customers off the product. Salespeople quoting from the manual would only reinforce what customers might perceive as a big negative. In the end, they decided to keep the break-in language innocuous and deal with people like me on an exception basis. Personally, I would have responded better to the dire yet truthful warning. On the other hand, I will concede that most of their customers, especially those new to hi fi, may not know the difference anyway and by the time they do, the speakers may have caught up.
Anyway, all is well now in my theater at last. My sincere thanks to all the members who contributed to this thread. I appreciate all your helpful and constructive comments!