There is no single "perfect" speaker for every listening preference. Every speaker design is a series of compromises.
Different people require and expect different performance characteristics from their speakers which is why there are so many different speaker designs and manufacturers.
There are some people who think Bose 901s are god like. There are others who have a very different opinion of them.
If there were only one perfect speaker there would be no need for this discussion group would there?
KLH 9s, like all speakers, have flaws. They beam. They have very little vertical and horizontal dispersion. When you are out of the "sweet spot" they fall off drastically so they are not good "party speakers".
They are VERY selfish speakers. Only 1 person (2 maybe) can listen to them, even as a double pair, and be in that "perfect" listening position. A double pair has no response below 32 hz and nothing above 19k.
They will not play loud, no matter how much power you put to them. They are not going to have thundering base like JBL/Altec/CV... They are not going to rip the cabinets off of your walls with their bottom end.
BUT
When you are in the sweet spot, they vanish and you are left with nothing but the performance, no speakers exist at all.
I believe that this old (1974) reviewer sums it up perfectly in this article
http://www.stereophile.com/floorloudspeakers/666klh/
When they say in their review conclusion:
To date, nothing we had found seemed to suggest that this system was worth anywhere near the $1140 the manufacturer asks for it. We changed our mind, though, when we heard music through it. This was the first time, since we started dabbling in high fidelity in the early 1940s, that we have ever felt we were really listening through a loudspeaker instead of to it; the system has a degree of transparency and detail that we simply did not believe possible.
This is the most nearly perfect loudspeaker we have ever heard, and we've heard every likely contender that's in commercial production. It does not favor some instruments over others, but seems to make everything sound almost perfectly natural.