Jerome, I hope you know I respect your opinions, but on this one we part ways, the speakers you are describing simply bear no relation to what I'm hearing from my M30.1's, and I'm honestly a bit baffled why you are getting such a poor result. I recall though in the early days with your M40.1's you struggled with the bass, until you sorted out the stands with the help of Pro Audio Bono. If memory serves, they were on Skylan stands too, and the general feeling on UK forums is that there are better options than Skylan, I'm happy with the performance on Rogoz stands, but many here like the open plan Something Solid stands.
Mine are in a relatively small room, and on a suspended floor, and bass issues have been a problem in here, which is in part the reason I ended up with the P3ESR's. My move to the M30.1's came about as I got a chance to buy a second hand pair from someone I trusted on a UK forum, at a price which would have allowed me to move them on a little loss if they weren't for me.....but they are everything I hoped, and have integrated into the room fine, they just need to be a bit farther from the back wall than before.
What I will say though is that the combination of my Snappers with their EL34's & the richness and warmth of the Harbeth's can occasionally seem too much of a good thing, I'm not sure I'd rush to try them with a 300b amp at 20w or so, whoever built it. I've got mine running with my Croft 25R pre & the Accuphase E450 as the power amp and trust me, the bass is impeccable

I love hi fi, but I also love old Studio 1 reggae, so they get tested! I'm probably going to try another tubed power amp in the new year, quite possibly either KT88 or even EL84 based (a pair of Mahi Mahi's might just be added). I was surprised by your results with your Nagra's, I would have expected that to work better than it seems to have for you.
I do have to raise an eyebrow at the "Design Fault" comments though, that seems quite a jump from one person not getting on with them to me. No speaker is perfect, they are all a compromise of one sort or another, but in my room the M30.1's sound absolutely wonderful, and in the 4 months or so I've had them I've noticed that, just like the P3ESR's, there is no part of my musical collection that is getting ignored, and that I always think is the most crucial thing of all
Best wishes
Matt