Dgad,
It's uncanny; you and I are looking for exactly the same thing at this point in the hobby. I too am extremely sensitive to distortion.
The -only- reservation I have about my MBL 101Es is that they too get congested at loud volumes during complex passages. They lose detail and smear and the soundstage becomes confused. This is true with any of the many amplifiers I have used with them, though my current amps tend to compound the problem (no amps have sounded less distorted or as wonderful under 93db, however).
I would like a speaker that, as you say, "You can listen at 100db and not even know you are listening so loud. No distortion etc. And everything remains stable in space with a transparency that is hard to believe."
I'm also looking for speakers that I can run with my 300B SET amps.
These two factors have led me to search for horn speakers using compression drivers. I ruled out the following a few years back (no offence to current owners intended):
Avantgarde
Acapella [great tweeter however]
Drivers such as Lowthers and Fostex
Back-loaded designs
The shortlist of speakers/drivers I would like to hear, in no particular order, are:
1. Sunny Cable H3W18 Majestic:
I think they use a GOTO driver in the midrange horn
2. GOTO
3. ALE
4. Cogent
5. Danley (pro-sound but interesting designs)
6. I'm open to suggestions as long as they don't involve asking me to revisit things that I have already ruled out or products that will be grossly inferior to the MBL 101Es in most other areas of sound reproduction.
Since I have no DIY talent or experience with horn or crossover design, I'm not going to buy separate drivers and horns and try to cobble something together. I'm also not going to hire someone to put something together that I haven't already heard. I, therefore, would have to hear a complete speaker system that sounds incredible in order to convince me to give up my beloved MBLs.