The closest approach...really

opinions greatly vary on this. It's really what you like that matters.

Some would say stacked quads, which give you more bass , would integrate better witha fast sub (10 inch speakers maybe) as it doens't have to handle as much freq area.

Well, let me specify that I was able to integrate them seamlessly (to my ears) in a relatively small room (something like 13x18).

The only caveat is that it took a while to figure out how to place them on the Gradient woofers. Once their feet are taken out, the ESL's sit on whatever flat surface in a slightly bent way. Well, that is definitely not the right position. They have to be perpendicular to the woofer in order to obtain the best sound. It is possible that some of the complaints I heard above have something to do with the position of the ESL's.

Mrtennis,
A seamless blend can be achieved. It depends on the room and on careful placement.

i have heard many combinations of dipoles and cones. in each case i have noticed the distinct sound of each driver. thus, for my ears there is a loss of coherence.

i would like to be put to the test, blindfolded, and listen to a pair of electrostatic speakers with a sub.
it would be interesting if i could identify that i was listening to a hynbrid.

Mrtennis, yes, that would be a nice test for everyone -- I think we're deeply biased in the way we listen to our equipment. In the end what matters is the survival test: how long has amplifier x or speaker y lasted in my system? If it's more than 1 year, then it means our ears really like it. If after a few months I begin to question it, then it means there is something wrong. In my case, so far the two things that lasted the most are my EAR 868 power amp and my ESL 57.