[jeffreybehr]

Are the 'old' 6-1/2" drivers used in the LS9s...
https://www.dagogo.com/gr-research-ls9-loudspeaker-review/2/
...good enough to justify spending anywhere from US$3K to $6K for a pair of LS9s? In spite of already having super-hi-quality SoundLab Majestic 745s in my system, I seem to frequently dream up something different to pis...er...spend my limited amounts of money on.. I love the idea that the Nines are true line-source speakers instead of the psuedo-line-source-plus-pointsource-tweeter NX-Tremes, but are the old bass/MRdrivers as good, overall, as SLs?  Will the L9s sound as coherent as the SLs?

I know--too many unanswerable questions, but some of you nice people will think of things, good and bag, about this question that I have not.

Jeffrey the Crazy Behr.

[Tyson]

I would snap them up.  There are certain things a line force can do that no other type of speaker can do.

[SoCalWJS]

What Tyson said.
I have LS6es that I love, but the 9’s are even better. They’re a special speaker IMO.
Worth it.

[S Clark]

In the GR-Research line, the Line Force speakers that Tyson has are clearly the best of the bunch.
But the LS-9's and the Super 7's were the next in line, and in my opinion, better than the current offerings. 
Like Tyson said, true big line source speakers do certain types of music better than almost any other designs.  Specifically, large orchestral music is their forte. 
They can create a concert hall in your (larger) living room. 
As for $3-6K??  If anyone is willing to sell them for that snap them up.  When they last sold retail they were 10K and you'd have a hard time finding something comparable at anything less.
I built a pair of LS9s several years ago.  I've only heard one design that compares (Super7) and only one better (Line Force)   But be advised they are big, and need a big space.