$3500 floor standing speakers used. What would be your choice ?

Used Vandersteens should fit the bill!

Vandersteen Model 2Ce Signature III | Vandersteen Audio

corelli, this is the first time that I "meet" someone who is familiar with these speakers. Yes, set up is critical, and if you push them too far they get out of control. But at moderate level with especially smaller scale acoustic music they sound quite good, acoustic guitar and vocals are convincing. VAC Avatar SE is an excellent match, Purist Audio cabling.

Devore Nine..

bjesien, thank you, this sounds interesting.

Tekton speakers..I usually don't like Eric's posts here and his preferences of electronics.

@inna Ah, brings back some fond memories. I had a pair of MG Rev60’s many years ago. A very nice speaker using classic Vifa drivers. Learned a lot about proper loudspeaker set up with that little floorstander.

Highly suggest you check out Tekton. Eric has many options in your price range. I think you would be floored by the performance of his speakers.. They would exceed your expectations by all the criteria you listed. See the parallel thread/review just posted by teajay on the Tekton Encore monitor. Then go to Eric's website to see his bigger offerings. You might do well to give Eric a call given the many options he offers.

Current speakers are Michael Green Audio Rev80i free resonance design. Let's say their sound signature is close enough to Grado RS-1 wooden headphones. I play at moderate levels, many kinds of music but not hard rock or big orchestras.

I don't tolerate bright or "stupid" hi-fi kind of sound. Midrange must be right or I won't listen. Going down confidently to 35 hz would be enough. Soundstage is very important, the space should be "heard" and felt.

I would search between 5 and 7K speakers used

https://speakerchoices.com/

A nice combo would be the Devore Nines, the original, not the new Super Nines. They lack a little transparency compared to the newer ones but it your not needing the last bit of resolution (which you won't get at $3500) keep your eyes open locally. They seem to go for under $3000 easy. 

What is your current speakers and venue? Would be helpful to see them. It is easy to create a virtual system with a few photos... that would be really helpful. What are yours tastes in sound?