I have a 4 gig card that works.
Just my opinion, but I believe that the higher capacities will work also.
I'd try one out, but my 4 Gb card is nowhere near being filled.
I have formatted a 4Gb card also with no problems. If you need more than that then you have a heavy workload..! Try buying 2x4Gb cards. That should last you the rest of your life...!
Sam metal,
depending on what you need with sample capacity it can be big enough. I use it strictly for sound samples assigned to programs.
But if you have samples for sequences or similar, it definitely isn't enough.
About expanding now available 96 MB, I highly doubt it will ever happen, Triton is long discontinued and there is M3, new flagship keyboard, so we are stuck with 96 MB.