Strangely, and now I am going to profoundly disagree with you, the ESL is easily the least diffuse speaker ever made, or at least that I have ever heard. Incisive like a razor - in fact - but also as smooth as silk when the music is.
Perhaps a poor choice of words? Although I'd hesitate to call them incisive. They have a gentleness and airiness to the sound which is very appealing, from what I've heard. I've heard three pairs over the years but I've never wanted to own them. I like the music to jump out at you where as the Quads paint a picture behind the speakers, which I think makes them so well suited to classical.
I've always used classic Linn speakers, Kans, Saras and Isobariks, and an interesting observation is that when you put enough Mana under Briks they beat the Quads at their own game! It's hard to believe that two speakers so different can sound so similar.