Trigger wrote: Can't shift either cup, tried a punch in one of the holes but it is just boring its way through the ally.
I wondered about making some flats on the cups and trying a big spanner?
look at the pictures of the assembly; there are no 'cups' there is a centre tube which is stuck in the frame, which was originally a sliding fit in the BB shell, not reliant on threads (which is the whole point of the thing).
Since the BB unit is scrap now anyway (and BTW shimano cranks fit OK on Mavic tapers IIRC...? and even if they don't fit perfectly they are not the only cranks.....) then using destructive means to remove the BB unit is now your only choice. I expect heat and a big hammer to be involved. Then you will need to repair the frame, probably.
BTW the bearing adjuster may well be seized up but it is meant to be turned using the appropriate mavic tool, not just battered with a hammer and punch. Even if it were not seized that would definitely wreck it.