"What's The Best Value Speaker In $5k-$10k Range?"

I'd appreciate some advice from those experienced with great speakers. I'm hoping that this thread will be valuable to lots of others, as well.

On to my question: What are the best value speakers you can buy on the used market in the $5k-$10k price range? I think it's time to get into something world-class for music, and I've found that in each area of life or hobby, there are gems available that might not carry the most popular brand name - or be the latest fashion - but that do deliver the best performance for the money.

I'd appreciate recommendations from any resident speaker gurus. Thank you!