Anybody besides the OP has managed to do this ? I've tried for weeks, I give up.
Used two cards, both SDXC 64GB, the SanDisk Ultra Mobile and a no-brand one from Amazon.
I used two different Optimus 2X, one running CM7, another running CM9.
The cards can't be formatted in the phones, they are simply not recognized at all.
I formatted them in Linux and Mac OS X, always FAT32, and always made a partition smaller than 32GB first, then tried ExFAT, full or bigger partitions, unallocated space in part or all, anything really. Nothing works.
Edit : the cards are fine, I can use then in Macs, PCs, DSLR and even a Galaxy Note. No problem.
Any ideas ? I'd think it's just not possible and the O2X hardware doesn't support SDXC, just SDHC, that's why I'm asking if anyone else can comment.