@holmz , Not at all. You ever tried an analog crossover on ESLs? Wel I have, several ones and they all turned out to be awful in the end. You can do it but there are far superior ways.
@drbond , 6 dB/oct is no where near fast enough to get the drop in distortion and increased head room I have been talking about. My filters are currently 48 dB/oct and the only way you can do that in an invisible fashion is with digital crossovers. I have been through every permutation of this problem some several times and have lost a lot of hair over it. If you do not want to use anything digital in your system you are better off without subwoofers otherwise they will drive you nuts and you will have wasted a lot of money. Subwoofers have to disappear into the music. You should not know they are there until a very low note comes along. In order to get the benefits of lower distortion and increased headroom, critical for ESLs you have to cross over in the area of 100 Hz which makes life even more difficult. Subwoofers also have to be placed in specific locations in order to work well. They are over 6 dB more efficient against walls and even more in corners. You also eliminate some (but not all) of the room interaction this way. This places them three to 5 feet behind the ESLs. In order to get the speakers aligned in time the ESLs have to be delayed a little. You can only do this in the digital domaine. Any other approach is a compromise you are not going to like.