Hi Sébastien,
It's not surprising that the SHL5s quickly run out of steam with only 8 watts. The Cary 805Cs are rated for 50 watts. Also, there are other manufacturers of 845-based SET amps that put out more than the typical single-watt ratings of 300b, 2A3, 45, etc. Art Audio and deHavilland come to mind.
Also, I owned a pair of Zu Druid Mk4s for a short time that I recall having a somewhat similar sound to the Harbeths. I can't whole-heartedly recommend them because that was a long time ago, and I could never get them to properly integrate into my room with my equipment. Just an additional path for you to consider.
It's not surprising that the SHL5s quickly run out of steam with only 8 watts. The Cary 805Cs are rated for 50 watts. Also, there are other manufacturers of 845-based SET amps that put out more than the typical single-watt ratings of 300b, 2A3, 45, etc. Art Audio and deHavilland come to mind.
Also, I owned a pair of Zu Druid Mk4s for a short time that I recall having a somewhat similar sound to the Harbeths. I can't whole-heartedly recommend them because that was a long time ago, and I could never get them to properly integrate into my room with my equipment. Just an additional path for you to consider.