All depends on how much you want to spend?
There are two companies that I know of that do proper 2 piece discs specifically made for the conversion, not cheap(£700-£800) but a hell of a lot lighter so very good if you're performance orientated as the MLs weigh a ton!!
I've changed my MLs for S5 discs for clearance reasons. S5s have a taller hat so I can mount my calipers a further 2mm inwards, they're also a bit thinner so a shade lighter than MLs, they bolt straight on with no mods at all, even the retaining screw lines up.
Only potential issue is the difference in thickness, 30mm instead of 32mm. If the pads wear right down the pistons might extend out too far beyond their recommended travel so I'll need to keep an eye on them over the next couple of years, won't be an issue to me as I don't do a lot of miles, rarely use the full might of the 18zs and I'm constantly messing with the car so can keep an eye on them. 2mm difference might not even be an issue but I can't find any info on a minimum thickness Brembo recommend so just something to bear in mind.
MLs are cheap, tried and tested tho, whats making you think of using something different?