Interesting, and you heard the Extrema's and the GH's through Krells...that says it all!!
( BTW, what subs were you using with the GH's???)
Who said so ? "It" was the recording.
Amps on GH's were almost always tubes - cj, ARC, jadis - although they liked the DartZeel's. And we used a pair of the old REL using the speaker preferred mode - Stentors or similar, do not remember and now JL Audio.
FIY, most of the time the Extrema's were used with ARC Classic 150 monsters. They also loved the conrad johnson Premier 8A.
Some people have the wrong idea of Krell electronics because they never listened to them in a properly tuned system. In the hands of knowledgeable people they could sound great with any Sonus Faber speaker.