In the mid-1970's one could purchase a combo-effort on the part of two of the premier manufacturers. Magnepan's inventor Jim Winey and Audio Research's inventor Bill Johnson got together--whether Wendell had anything to do with it is moot--and developed a tri-amped system that used an external (tube) crossover. The Typmani speakers were in three parts...kind of what Mr. Winey's son has gone back to recently, with superb results...and they were driven by three+ (you could bridge the amps and run 6 if you wanted to) Audio Research amplifiers run through an Audio Research SP-3 pre-amp. The amps were of the D-76(A) vintage, which was then doubled into the D-150--still an awesome amp all these years later. The crossovers were both passive (PC) and active (EC-tube), and one could select a number of ways to set this up. More importantly, HOW DID IT SOUND?? All that technology is fine, but if it does not sound like a live concert, or as close as possible to one, then it is of little value.
The good news is that the SOUNDED AWESOME. Set-up properly in a good room, this was the ultimate in those days. Today, I would guess that the new Magnepan 3-part speaker set driven by quality amps is probably somewhat better as the technologies of all these components has improved since the mid-1970's. In any case, it sounds better than any box speaker system, so I don't think speaker design is in the tank today. Most designers use conventional drivers, but I constantly see engineers trying different materials, etc., to get the accurate sound they are seeking. Too bad that Magnepan found a way to do it better than cone or electrostatic designers have so far...but that doesn't mean engineers are not hard at work looking for the "next big thing."