I am new to this site, but wanted to put in my two cents about the Klipschorns and how to get the best sound out of them.
My story. I bought a pair of khorns about a year ago and was ready to experiment with different amplifiers until I found one that would work well and sound good to my ear. I tried several modern amplifiers upto a $1000 range. I did look at the McIntosh as well since several my friends have them in their home theaters and they do sound fantastic, but I did not want to spend that kind of money. So I set a $1000 budget for myself and went amp hunting. I bought tube amps and ss amps of modern day era, which are hard to find to begin with, because the sales people at most stores these days think that an all-in-one receiver is an amplifier. So I bought and returned a couple actual amplifiers and sold others because none of them complemented the khorns. These amps did however work fine with my other reference series 5.1 sound system, just not the khorns.
My research finally helped me reach a decision that I need to get back to the vintage amplifiers. I had read that a good amplifier match is a must to enjoy the khorns. After reading countless threads and parises about the khorns, I was surprised to find very little information on amplifiers that work well with their khorns. And yes, if you have used amplifiers that were not a good match, you do hear the hum, lack or bass etc. as described by the host of this thread.
So again, I went hunting for vintage amps and pre-amps. After going through a handful of those, I finally came up with a couple of great amps from the old days that work really well with the khorns. Very musical, excellent bass, fantastic soundstage, the highs and lows-amazing, even though my khorns have a 2 inch gap from the corners and are not totally flush. I do plan on experimenting with Paul Klipsh's suggestion of false wall and will let you know how that goes.
And finally the three amplifiers that I tried that worked incredible. They all happen to belong to the same family:
Sansui AU-717 - I have
Sansui AU-9900 - I have (This is Sansui's professional series. A bit hard to find, but worth the wait and money)
Sansui AU-11000 - Bigger brother to the AU-9900
Sansui AU-20000 - Bigger brother to the two mentioned above.
McIntosh-275 - Tube
The later three are of the same family. Only difference is the power output.
Any one of these units will do a fine job. Only thing to remember is that due to their age, they may have to be recapped, since capacitors etc. have a finite life. This will cost around $300 for restoration.
In my case, I did have the AU-717 that needed recaps, but the AU-9900 was in excellent condition every which way.
So, here you are. I am sure there are other options in amps, so please share if you can. I have put in my two cents.
NOTE: With the Sanui amps, I did not encounter any of the issues mentioned in the editors findings or what I encountered with the modern amplifiers. Perhaps more research can be done on this.