Harbeth 40.3's. Should I buy them?

Definitely risky with your room and amp. Your amp is very nice but has a 120 watt rating at 8 ohms 1Khz. Full bandwidth is more like 70 watts and probably no more than that at lower impedances.

The Harbeth 40s really need authoritative control of their large woofer or the bass will lag and be tubby sounding.

To get the best out of them requires a robust solid state amp stable at low impedances. Not that the Harbeths have low electrical impedance but the 12" woofer demands a solid reign.

Last time I heard them they were driven by Vinnie Rossie L2 signature MOSFET monoblocks and they sounded fantastic.

Time before that they were driven by a Parasound a21 and sounded bloated as heck.  

coppy777 - I’d never mention B&W for speakers that Rock.

I’ve owned several B&W’s over the years, and have had my Matrix 801’s for 25 years! I love them, and they do many great things, but they just barely rock. Dire Straits & Pink Floyd sound amazing, but compressed pop & rock is not the best. My Tannoys are fun speakers. I’ve got 15" System 15 studio monitors, and they do ROCK, but LF drops off at 45Hz. They need a sub. My 3rd pair of mains are Martin Logan SL3’s (w/new panels). For 20 years i’ve been swapping these 3 pairs in & out of my living room every few months, and they each do something special for me. And all sound very different from each other.

I’ve always admired the Harbeths, but when I hear them at shows, I am underwhelmed. As with any good speaker, I think they’d do many things really well, and some things not so well. I highly recommend having 2 very different pairs of speakers that you can rotate into your system, if you have the storage space. I’d rather own two very different $5k pairs than one $10k pair.

@avanti1960

... is correct - the Harbeth 30 and 40 series require a good SS amp to bring out all their capabilities and sound their best - just as Harbeth "suggests" - they typically show them driven by Hegel SS amps. As I noted before, mine didn’t sound great, until I got the H590 to drive them properly. Now they do!

Though, I like their sound with "all things acoustic" - I don’t listen to rock much. As I noted, with the "all things acoustic" they are superb and sound very much like Quad ESL 57’s - which are the best there is with that type of sound (when set up and driven properly).

Though... as I noted previously... if... I had the right room for them (and could manage them physically)... I would have the Legacy Audio Aeris, or Focus SE / XD’s - which do it all as well as it can be done - Superb! They may not sound as much like the ESL 57’s with the 57’s "rich, liquid sound"... but... the Legacy’s are the next best thing for a wide range of music, bass, percussion and dynamics... when you want that!

I’d recommend big ProAc’s D48R sound amazing big and fast and visually not weird or ugly. You have the perfect amp for them ProAc’s love tubes! I’ve owned lots of speakers and I’ve always come back to ProAc’s! The D48R is the top of the response line. There’s also the K series much more $$ but better. 
 

I also like the Dynaudio. I think that the Dynaudio have the best Soft Dome tweeters. If I had the cash the Dynaudio Confidence 30 would be a real contender. But I really love the ProAc Ribbon tweeter. 
 

The Vandersteen Quattro Wood CT are a Fabulous speaker. A must Listen!

I think the Magico’s are also Wonderful even the smaller A series are awesome the A3 . Get a listen!!

HTH

@bassdude ...As I noted before, mine didn’t sound great, until I got the H590 to drive them properly. Now they do!

+1 what @avanti1960 said too.

Harbeth, Spatial, Legacy, Quad 57s - all can sound good when paired up with robust amplification combined with good room setup. Having tried building pseudo replica ProAc floor standers years ago, how they can pair up so well [as @axeis1] suggested, with some lower power tube amps - is still quite interesting to me.