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

Hi zwango!  Try the Starke AD4.320. I have two of them. Superb sound. WAY less than $2K. Never heard a better amp. I also have two of the Purifi Audio EVAL 1 packages. These are the best amps available. Great reviews. No kidding.Happy holidays.

For (nearfield) listening the ABH2 will be the best. And, the transparency will enhance the ’British roots’ of the Harbeths as pointed out above whilst keeping tight woofer control. Oh, be sure to get the inexpensive Benchmark Media cables especially if you are in a home office environment with I assume with computers and so on. Finally, it has the best volume control of the bunch - 0.5db increments. Makes a soundstage difference. BM has a 30 day money back trial and no-one sends them back.

Which preamp are you using? You can tailor the ABH2 to the source output. It runs cool and sounds like it is not there.

I just replaced a pair of Constellation Centaur Mono with the ABH2s bridged in mono.  They are fantastic, punching way above their weight and cost.  Extremely detailed and dynamic. Huge soundstage.   I’ll be using 4 of them and a Pass XVR 1 to biamp a pair of TAD R1s.  Will update as that project moves along.  

Ayre or Bryston. 
 Happy hunting.

I have owned one and then two of the Bryston 4B3s. They are wonderful amps with lots of power. But for an office they are big. If you said you were looking to drive Maggies, these would be my top recommendation. But I also currently own a pair of Benchmark AHB2s. Very transparent. Very cool running. More than enough power. You can get nice speaker cables with Neutrik connections for them from Zu Audio either on their eBay store or their website. Those would be my top recommendation for the Harbeths. If you are looking for a preamp consider the Benchmark preamp. Small and transparent. Goes great with the AHB2(s) that will bring you clean SQ (that also measure great) in smaller form factors. Enjoy!