Regarding comparing speakers that are next to one another... I agree there is "some" effect, feel free to disagree with me, but for ME, I can easily hear the major differences in designer priority with the speakers right next to one another. When comparing cables and looking for subtle 1% differences, then I can agree that minor factors like this can skew the results... But for this test, the differences that I hear are not significantly impacted by the other speaker being there. I have confirmed this by moving the speakers out of the room.
With that being said... both of these speakers are really, really good sounding. Neither is "better" than the other in an overall sense, but definitely, one of the two can be "better" for any given person depending on listener goals and priority.
Which of these two completely different designs you will prefer really depends on your answer to this question:
If you had to choose, what is more important to you? - a BIG powerful and macro-dynamic sound (ultra wide and deep soundstage, MEGA capabilities with bass pressure and big-scale dynamic swings), or a tight, clean sound (pinpoint imaging, absolute clarity, ultimate transparency)
It probably goes without saying, but to be extra clear, the LS6 are the first speaker, and the Merlins are the second.
In a perfect world, I would play my less than 100% recordings on the LS6s, as well as my rock and big scale classical recordings, and play my best recordings on the Merlins, especially smaller ensembles.
I want to be ultra clear that the LS6 are not vague, muddy, or anything like that. The highs shimmer with those ribbon tweeters, and they are actually quite clear sounding. Much more transparent than the Dynaudio S1.4s that I had before. They get probably 90% of the Merlins clarity, but they aren't quite there.
With the Merlins, again I want to be clear that they cleanly extend down to the mid 30hz with the BAM in my room. They throw a great soundstage as well, probably a more accurate one, but they don't do the uber-big scale presentation and dynamic swings of the LS6s.
So instead of invalidating either speaker, for me, this comparison only validated the very real strengths that each design has. Which one you would prefer ultimately depends on your goals and your room. If you have a smallish room, the LS6 simply won't work, unless you go nuts with treatments and/or EQ out bass problems.
It was not an easy choice, but at this point in time I've decided to go forward with the line arrays. I'm working with Rives audio to build a dedicated 2-ch room in my basement. (I have moved since the picture in the original thread was taken.)
I would not hesitate to strongly recommend either of these statement designs to a friend, assuming that I know what type of sound they are looking for.
Hope that helps!