Thanks for the response @arafiq I wasn’t too surprised that the Supernait 3 sounded poor with the Harbeth SHL5+. It’s the same experience when I tried the Nait XS on the SHL5. Somehow the Naim integrateds are not very good in my book. Perhaps they are good for easy to drive speakers only.
The Luxman L-590AXII is truly a marvelous amp. I’ve not tried a lot but this one is really something special. Refined, delicate and nuanced - these are the keywords I would use on the L-590AXII. The bass may not be the punchiest or most visceral but it’s clean and pure. In other words it’s a tight, defined and nuanced bass quality made possible by the low coloration of the amp. Other amp designs which produce more bass sound more colored to me with their forced presentation, masking some of the detail in the bass and sounding slightly unnatural or less nuanced.

