Ron, your listening levels and amplification are very appropriate / safe. So something else is going on, perhaps bad drivers, but sometimes cables can induce amp misbehavior that adds stealth distortion. I can't troubleshoot, but I will try to find out the service history of those drivers.
Prof, that cliché is true. Tube amps clip softly, without much hash, and therefore are far more gentle on speakers when driven hard than most solid state designs.
As an aside, I have played hundreds of Thiel speakers for thousands of hours, often in very demanding and loud situations, and have never blown a driver . . . I have also seen hundreds of "blown" Thiel drivers and in the vast majority of cases the voice coils are burned, which is (practically speaking) only caused by distortion (the driver will produce ear-piercing volume without damage given a clean signal.) Those burned coils are user-damage, but Thiel generally covered them ONCE under warranty as good will. Legitimate manufacturing defects include subtly mis-routed lead wires, magnet-position and/or suspension mis-alignment or glue failure, etc. Those are generally batch problems and result in instant failure (broken lead) or immediate voice coil rubbing. If it's defective it will fail quickly.
Part of my upgrade project is thermal management, which is generally ignored in hi-fi, but is very important in sound reinforcement and pro-audio. Heat is a real enemy. It can shift crosspoints radically, which adds substantial stress to the system. A 3KHz tweeter crosspoint can migrate to 2500, admitting damaging low frequency signal to a driver which is vulnerable due to the concurrent high-power situation.
So, I am mounting all resistors in heat-sinks mounted to buss bars to dissipate waste crossover heat. My CS2 2 workhorse is getting an aluminum tube spine up the back of the cabinet to sink those buss bars as well as mounting an aluminum tube from the back of each driver which conducts heat as well as provides more mechanical stiffness to the driver mount. I am puzzled that Jim abandoned aluminum voice coil formers for nomex; probably for lower mass and smoother high frequency extension. But thermal conduction was traded off. This note is just to let you know where my investigations are leading.
BTW, I have a pretty big pile of foil coils, resistors, wire and caps, plus the Clarity Caps are finally on their way. I'm especially excited about a CC custom polypropylene cap we have developed to replace all the electrolytic caps. I'll be comparing the new CC to the ERSE PulseX Polypropylenes in those applications. Either way is a big step up from the present electrolytics in the shunts. Progress is being made.
