the smoothest sounding speaker

I hate to argue with you Lou but in my experience it is the loudspeaker that is most often to blame for fatiguing sound. Before I found and fell in love with your DA-1's, I heard countless speakers--most often connected to top shelf electronics (both tube and solid state)--and often found them to wear on me after a relatively short period of time. There are very few speakers out there that get things so right that you can listen (at volume) for hours on end and never feel oppressed. I'm not saying that poor electronics can't mess up an otherwise good speaker but for the most part I think you need to get the loudspeaker right first and foremost. I think your success in this area transcends choice of electronics and source components.

Here's one When the drivers like this have incredibly low distortion, and the design is well implemented, you get a non-fatiguing "listen all day" type of sound

I think (as of today) driver distortion is my biggest detterent to enjoying the music. I can live without all the detail, bass, or treble, but if distortion is high.....no way.

and the kit ZRT

Low distortion
Wide even dispersion
Flat frequecy response
Well Damped and Excellent transient response ( & no dull compression)

The speaker that I have found to strike the right balance between resolution and smoothness is the Merlin VSM-MXe. The other speaker that seems to be as good are the various speakers I have heard from Verity; if I didn't own Merlin, that would be the speaker line that would most interest me. I also owned the Vandersteen 3As/2wqs, but the Merlin was an improvement in the area resolution and micro dymamic detail. The Merlin uses the Dynaudio Esotar tweeter and I imagine that is a reason for its smooth upper frequencies. Of course, using tube amps doesn't hurt.