Hello, Orfeo!
I'm assuming you're in Europe - Italy, perhaps?
Thanks for your interest in my system. The Monitor 30s I owned were the original 30's, and I loved them, for all the reasons you state. I'm curious as to where you heard the LS 5/8's - at a dealer? Perhaps the room acoustics were not ideal, but in my room, I feel that the midrange of the 5/8's is glorious! If they have any weakness at all, it's the fact that the big driver does cover a wide range of frequencies, and it will sometimes "harden" up in the region of 1800 to 2000 Hz or so. Overall, I find these speakers to have a bit more life and energy as compared to the Harbeths, and the low bass, when it is actually present in a recording, is astounding! They have been a game changer in my musical journey, and if you can afford them, I highly recommend them. Hopefully you might find a dealer who would allow you to audition them in your home for a week or so. I bought mine sight-unseen, sound unheard, but they have worked out perfectly in my home.
Best wishes in your musical pursuits!