I've owned stock Klipschorns for a number of years and have been very happy with how they sound. This past weekend I decided to do try some upgrades; replaced the AK-2 networks and K-77s with B&K A/4500s and CT120 tweeters from Bob Crites.
I was expecting a subtle difference in sound quality but was blown away by the improvement. The low end feels tighter, mid/highs are clearer and everything sounds more cohesive. Stereo imaging was much more focused.
I don't have any measurements but I did some listening comparisons by playing mono through the left (pre-mod) and right (post-mod). I asked my wife which she preferred and she was quick to chose the one that had been upgraded. Not scientific by any means but I'm very happy with the results.
Having lurked here for many years I figured it was time to contribute something back.