Best 40 to 50k used speakers

If you have the opportunity to audition the A5 , do it !!! 
I will also recommend YG Hailey , if you're tast is in the aluminum corner ...
Mine is ..

For that kind of money you could get the monitor audio platinum 500 ll for $30,000 brand new and those speakers will beat speakers that are three or four times the price. Check them out.

Dude jump on somthing ASAP!!!

Another vote for whichever Focal Utopias fit your room.
I have the Stellas myself, the EM bass is just effortless, even in my difficult room (concrete floor, patio windows behind speakers)

Amplification?
Has to be Boulder. Truly a marriage made in heaven. So rich, textured and authoritative. But above all, musical.
This combination is truly on the side of the performer - producer

My vote (purchase) was for Raidho D-4.1s. Last Raidho model with pure Borresen DNA. They are beautiful and sound great with my wildly eclectic musical choices. I have Focal Utopias too, and while the Focal sound is really good, it can’t compete with the Raidho/Borresen speed.