???What's The LEAST Expensive "End Game"Amplifier You've Ever Heard???

The Neurochrome Modular 686 had been heard in use in a £200Kish system, where a £50Kish Amp' was removed. The System did not need the £50K Amp to be reinstated to get it to perform at its best.

Both Amp's were very comparable with subtle differences.      

I got my Hegel 390 new for 4500. I can’t imagine a better deal for what can be an end game all in one system. Just add speakers. 👍🏼

And a preowned h590 even better at 5k. 

I love my Arion Audio S500.  Shoebox size digital switching amp designed and built by Mike Kallelis.  500 watts per channel, super clean, neutral sound.  Plus, it weighs only about 22 pounds!  Price should be under $3000.  A real bargain, and I can't see myself ever replacing it in an attempt to upgrade.  If it ain't broken...

Amplifier Circlelabs A200 -  on the SAME level as Gryphon

The Pass Labs XA25 is one of the most 'transparent' amps and a reference for many reviewers. Audiophiliac, Stereophile, Absolute Sound. I have one paired to Harbeth 30.2 40th and it is a match made in heaven.
Last week i was auditioning speakers and the store owner told me that a customer had recently changed his entire set up 5 times more expensive to go with the XA25 because he liked it so much. 
At about 5k USD , you cannot go wrong. Built like a tank, sound like velvet.