Any advice? Parasound A21, Ayre V5xe, Benchmark AHB2, or Bryston 4B3?

...........a precision to resolve high frequency detail, imagery and delicate subtleties that give the sense of air and space..........

That's exactly what I appreciate about the AHB2!

Check out Hegel. They're coming up somewhat regularly on ebay and here for ~25 to 40% off list

we just purchased a hilo by parasound and love the unit.  you should audition what you like at the $2500 to $3500 price point but would not go wrong with Parasound in my opinion.

I have an all Ayre sysrem... all of their components sound best when you use them in balanced mode. ..never had any issues with any of their stuff.  Recommended

I have owned an A21 since January and only heard it through my Martin Logan speakers, so cannot compare to other amps/speakers as others here can.  I can say that my amp does not run hot . . slightly warm only . . but I have it open to room air and would recommend that.  

For that price range, Parasound has an updated model with more power, the A21+, which might be a better comparison to the other models you are looking at.  Normally $3,000, I’ve seen the A21+ on sale recently for about $2,500.