Ive never had a problem with lathering a MB soap.
I always use Prorasso pre-shave
I use a Boar brush (Omega 10005)
Always bowl lather.
Soak brush in hot water while showering, hot water on top of soap in bowl for about 3-4 minutes, squeeze brush quite hard, empty water from top of soap bowl and squish the brush into soap, I find pushing down on the brush until the bristles go to the outer edge of the bowl and then spin the brush in my fingers so it goes round and round with the occasional pump up and down, this gets all the soap right into the centre of the brush, maybe do this for 25 seconds, any longer and there is just too much mess! Scoop all excess lather out of soap bowl and then transfer to my shaving mug, adding a few drips of water from my finger tips as needed, never needed too much water and never takes more than 3 minutes to create whipping cream like lather.
Usually enough to do my 3 passes with enough left over to do a couple more if needed.
I live on the coast near Minehead, I suppose this is soft water?