The handbook does actually say 64GB limit I think - which is what I have in there (though only about 31GB of stuff on there). 2TB is the maximum supported by the SDXC standard, but that doesn't mean that every SDXC device will support that capacity.
For those that have the 128GB card - I'd be interested to see what happens if you fill it up more than 64GB, whether everything on the card is playable etc. It may well be, but the manual does state a limit.