You didn’t mention the amplifier used but that too makes a difference. As you probably know, Harbeth speakers are easy to drive and sound quite good with most suitably powered amplifiers. This would include certain British solid state integrated amplifiers. I have used the P3 speakers with Naim Nait XS2 and SuperNait2 integrated units. The SN2 added some needed warmth and bass response but I still wasn’t satisfied. I recently tried three other high quality integrated amplifiers, two solid state and one tube. The clear winner was the LFD Zero Mark IV, which had much better bass and PRAT than any other amplifier I have tried. The LFD also had a more natural, mid-hall presentation that sounds as close to real as I’ve ever heard in a stereo system. The LFD/Harbeth combination is truly extraordinary. The lack of remote was initially a turnoff, but I use a Logitech WiFi remote to control my source and it works great.Interesting that you find the LFD Zero Mark IV to have better bass and PRAT than the Naim Nait XS2 and Supernait2. I have tried the LFD Zero Mark III with the Harbeth and there is certainly a great synergy in this combination. I have listened to the Nait XS with the Harbeth and share the same sentiment that the Harbeth sounds nicer and more sublime with the LFD. Apart from the bass that is more prominent with the LFD, the midrange and highs of the LFD have a certain tube-like glow to it. Somehow the Nait XS didn’t possess the same verve and rhythmic drive when compared to the LFD and took a flatter / monotonous sound. A caveat is I did not have a Hicap connected to the Nait XS when I listened to the amp. Nevertheless, there is no denying the fact that the LFD gives the best of both worlds in combining tube-like warmth with speed, slam and dynamics of solid-state, a rare feat to achieve indeed. In this sense I agree that the LFD/Harbeth combination is unique and remarkable.
I am currently using Naim NAC202/NAP200 + Dual Teddycap with the Harbeth SHL5s and I can vouch for this combination as well. The Naims may not have the wonderful tube-like glow of the LFD but the rhythmic pace (PRAT) is on another level compared to the Nait XS. Music has a certain groove to it as the crescendos from silent passages are all delivered remarkably well (good macrodynamics). After living with the Naims for more than 5 years, I now have an NAC282 on the way after being influenced by the group on the Naim forum just recently. Initially I did not have plans for an upgrade but the enthusiastic group on the Naim forum appears to have succeeded in convincing me to go up the Naim ladder. Maybe I should stop visiting forums so that I can stop buying new gear.