Electronics for Harbeths -- $5-10K

One new candidate is Ayre Acoustics's Series 8 line. The new VX-8 power amp just got a great review in Stereophile, although the corresponding preamp may not be a great fit.

However, the updated EX-8 2.0 integrated looks pretty close to a perfect match, at least on paper.  The $8000 analog-only version (it'll sit behind an external DAC/streamer) weighs a mere 25 pounds, pumps out about 135wpc into 6ohms, has all the connectivity I need, including HT bypass & sub out) as well as unique features like the ability to disable individual outputs. 

That last function is especially important because the Harbeths will also be used as the FL & FR speakers when playing multichannel content.  That is, a multichannel source will be decoded by an existing A/V receiver that will forward the front-channel signals to the new amp.  This means -- think about it -- when playing stereo content from a turntable, Tidal, or SACD, the new amp will drive the sub.  The receiver wouldn't even be on.  But when playing surround sources, the sub will have to receive a multichannel-mixed LFE signal from the receiver & the new amp should not be sending a second signal simultaneously to the sub. (I have a powered MartinLogan sub that can autoswitch between any of three line-level or amplified input signals, but should never receive two inputs at the same time.)

So from a functionality standpoint, the Ayre is the only option I've found that can do everything I need.

What I don't know -- and yeah, this is the same old problem -- is whether the EX-8 2.0 is a good fit with the Harbeths sonically.  Stereophile's review of the original & 2.0 versions are pure raves -- praising even the built-in headphone amp, to my surprise -- but hey, so are half the reviews in the magazine. 

So although I've made progress finding a credible candidate re: functionality, I'm still at Square One re: sonics.

Maybe I need to start another thread with a title that specifically asks about the Ayre/Harbeth combo.  Unless any of the people here have tried that pairing themselves.

I have the HARBETH M30.2 XD standmounts with an ATC C1 Sub Mk2 Subwoofer.

My best-of-breed integrated amp to drive them is a REGA OSIRIS integrated amp that is a bona fide “soulmate” contender and no pretender, that satisfies your amp features .wish list .

highly recommended

https://audiofi.net/2012/08/rega-osiris-punching-heavy/

https://everydayaudiophile.com/2019/12/23/rega-osiris-a-dual-mono-champ/

OP, regarding the Benchmark, like everything it comes down to synergy and personal preferences.  Can the Benchmark compete with more expensive gear?  Absolutely.  But, it’s not pretty to look at if you want something that looks like Mac, Lux, or Accuphase!  That said, back to synergy, I found that the Harbeths have their own nice, warmish, round sound.  The Benchmarks are super neutral sounding, so you get what the speakers have to offer without any additional coloration.  The star of the pair is probably the preamp (LA4).  Very high resolution and lots of flexibility.  I prefer a neutral sound more than “tubey”, so that may be why I liked the Benchmark.  But overall I think the synergy is great between them and the Harbeths for the reason I mentioned,

@cundare2  I posted my comment early this morning (couldn't sleep). My first post attempt stated my experience at an audio show where the Harbeth 7.3 was mated with a Plinius Class A SS amp. Sounded heavenly. This first iteration was deleted accidentally and the second one is what you see.

At any rate, you can't go wrong with BAT. 60-day return policy from Uncle Kevin at Upscale. I've owned this integrated twice and currently use a VK-33SE/VK-255SE combo.