The Magnepan fuse block contains ferrous (steel!) parts, a terrible idea. Maggies can absorb a lot of power with little chance of damage, except for their fantastic ribbon tweeter (found in the current MG3.7a, 20.7a, and 30.7).
I just by-passed the block in the bass panels of my Tympani T-IVa, leaving it in the midrange/tweeter panel. The ribbon tweeter is not that expensive to replace, so some owners bypass the fuse block protecting it as well.
The holes for the stock binding posts in my T-IVa's were just (and I mean just) a hair smaller than the size of the Cardas posts. The gentle use of a circular file (merely running it around the circumference of the hole a few times) enlarged the hole enough to allow the Cardas posts to be inserted.