well, it is a bit hard to find actually.. we have tested up to 64GB on DB410c ourselves. The kernel output seem to indicate SDXC support
mmc1: new high speed SDXC card at address 0001
mmcblk1: mmc1:0001 62.5 GiB
So I am tempted to say that 128GB should work as well.. we are still trying to chase down the information, but I am not sure we will get it..