Joe... As you already know I am a HUGE fan of Harbeth speakers.
I owned all models in the Harbeth line which include the Compact 7ES-3, SHL-5 , M30 and now the M40.1
The Harbeth presents music in a wholly natural way without any listening fatigue. The midrange has a nice warmish feel and the highs are sweet, smooth and extended. Although there lies a super-tweeter in the SHL-5 that in the mind of some folks would extend the high frequencies in having more clarity and detail, the speaker is not the last word in transparency. The treble does not sound as airy or extended as some other high-end speakers with ultra-revealing tweeters constructed from exotic materials, nor do they impose an intimidating stature compared to other physically large speakers with high-quality gloss finish standing over 6 feet tall. This is neither a disparaging comment nor criticism towards the SHL-5 as the sound it produces is what that matters. The lack of transparency and detail can be seen as a favorable trait that may appeal to listeners with specific listening preferences. This particular inherent characteristic of Harbeth speakers, I believe, has been fundamental in creating a zero listening fatigue which in my opinion is vital in contributing towards the musical enjoyment with many hours of listening pleasure.
The M30 and M40.1 are true monitor sounds and the SHL-5 is more for home use.
However they still share the same house sound as sweet voice and boxy sound. Once you play the Ben Webster's Soulville you will know exactly what I meant.
I used to owned the Naim full system. ( Nac 282 + Nap 250.2 + CD2X + Hi-Cap ) as Jock mentioned they do go well with Naim . However with my taste the mono blocks of Mc275 blown them away by far.
I still paired them with the M40.1 with excellent result.
You CAN'T go wrong with your GAT+ART combo. You will be bath in music for sure. Play any female vocal and I bet you will find the whole new level of Mid-range and voice sound.
One thing ...... Please Please don't ever prejudge the Harbeth speakers with 30 mins of listening session.
Hope this help. :happy: