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

If you're into tubes, Raven Audio makes one hellava great sounding integrated amp... Check out the Night Hawk:

https://ravenaudio.com/product/nighthawk-mk3-tube-amplifier/

Tride labs 2A3 mono blocks, with the right speakers they are sublime. 

+1 on the Synthesis integrated amps, the A40 or A100.

I've had a ton of amps, both integrateds and separates, and the Synthesis has ended my in interest in finding anything "better." The onboard DAC is also very capable, although I will admit that my Lampizator Horizon is on another level, as it should be given the discrepancy in price. Together, they are just incredible.

Hegel H369/390 if paired with Harbeth.

Aesthetix Mimas for full range, its optional DAC and phono cards are sonically fantastic high value for an integrated.  

The Parasound A23 is certainly not an end-game amplifier. None of us likely have enough exposure or information to confidently declare any piece of equipment as truly "end-game." However, I've owned the A23 for years and have never considered switching, even though I've retired my DAC six times.