I owned a pair of Heresy's way back in the 70's. Ialso owned a pair of Chorus's for about 6 months a couple of years ago. However, I know a Klipsch dealer fairly well and have heard the La Scala's, Belle's, and K-horns. The La Scala's and K-horns use the same length midrange horn, while the Belle's have a much shorter midrange horn. All use the same mid compression drivers however, assuming they are all of the same vintage. The Belle's go noticably deeper than the La Scala's, approx. 10 hz lower (the La Scala's really don't go below 50 hz), while the cornerhorns get down into the 30's. To my ear, I was never a great fan of the Belle's, as I thought them to be too harsh, maybe due to the short midrange horn (?). As to what type of amplification to use, I cannot offer a valid comment on SET as I have no personal experience with them, but logically they would seem to be a good choice. This I do know, however. If you want to go SS, try Macintosh. While not the most deailed or fast amp out there, they do a very good job of "taming" the horns. The best Mac amp out there IMHO, the Mac 2255, but hard to find. I do need to comment that I am really not a fan of horns or Macintosh equipment anymore, but if you like lots of sound with big impact or listen to mainly rock, then Klipsch speakers will knock your socks off. Hope this helped, if only a little bit.
Bill
Bill