What used speaker would you buy with $20,000-$35,000 and why?

I will mention however that Electro-voice has been building sub-woofer's for stage use with the same woofer design in a cabinet for the last 20 year's,  it's a bass horn!, that is exactly what the bottom half of the lx521 is! , cool with me,  I was a professional musician most of my life,  cerwin-vega and JBL first invented the horn bass speaker system's decade's ago, so some of this design was borrowed from the mentioned of this post .

You really need to hear anything by Acoustic Zen. I also like Raidho, but they are rather expensive in comparison.

Audiotomb, my amps are SS 600 watt mono blocks. Suffice to say they are matched well to my current speakers and are of sufficient power to drive anything. My pre-amp is a tube. I don't want to mention a brand lest the brand critics muster themselves to take us off-topic (I'll PM if you'd like).  

It is true that listening is highly subjective and that the speaker-listener interface is perhaps the most subjective of all. Ultimately, that too is subject to all of the previous components, so it is the interaction of the parts that produce the whole (hopefully one that is synergetic). 

Today I found out that the sub-floor consists of 2 x 8's floor joists which have a span of 14 ft. Can anybody say "Ouch"!? No wonder I have perceived a lack of bass punch since I've moved my equipment into that room. It has ideal dimensions, but pitiful mass and stiffness. The minimum for that span should be 2 x 12's (preferably supported).

I will be remediating the situation with piers under the subfloor etc. I'm open to any advice you guys have on what should be done as well. The work needs to be done for the foundation of the old construction and not just for the sound. Obviously, I can't tear the entire part of the old construction down, but I plan to have concrete block supports and a beam placed under that room (and the rest of the old construction) to make it vastly stiffer. 

I like the Vandersteens. I've looked at a couple of Joseph Audio speakers (visually) and, while I haven't heard them, some of the visual cues are similar between them. I'll bet similar models sound quite different. 

Regarding the Linkwitz speakers... even after hearing the various YouTube videos of them... I was a bit of a skeptic... until... I got my Orions driven by a good set up.

Now... I'm a believer!  

There are very few speakers that can match them (Orions or LX521s) - they do it all... as well as it can be done.

Sonus Faber Stradavari. They do not come up often but when they do they are often in the mid to low 20's. They are a wide format, so you need some room for them. Glorious, from the old Sonus Faber line. But, then again, I am an old Sonus Faber junkie.