No Magnex are crap to be fair, all exhaust manufacturers are not the easiest to deal with, you can call them though.
Alternatively look up someone like Longlife exhausts, they just custom make systems, boxes and centers I'm sure they'll fabricate it for you, you won't really join in to the original due to no male / female ends as it's one piece, go for a custom one, I got quoted £399 for a full system so shouldn't be too much just for a centre.