After doing a fairly rapid search for an expansion board for the X32 Compact, I came across this well priced and quality-build ADAT expansion perfect for my studio requirements (replacing a lightpiped Macke d8b was a task in itself) - seeing that the X-ADAT by Behringer was at a great price already, then stumbled across Klark Teknik's version, which basically is the same bar the manufacture print on the back plane - and after a little more reading confirmation this works in Midas M32 and Behringer X32 mixers - superb!
Swapping out the X32 USB board and plugging this is is child's play (make sure you get the board to sit on the two runners at the opening for a very fast plug-n-play). Two screws on the side, pull out, push in, screw in, plug in your optical cables (check your outer plug size as mine were a little larger and I had to do some surgical 'shaving' - maybe the sockets are a little closer than normal but due to the real-estate available), and turn on the X32, fires up and accepts the card in seconds. Workclock is solid too, just match up your sample rate to your system and you're golden.
Summary - if you're looking for a suitable expansion without breaking the bank, you can't go wrong with this one!