B9S is a bootloader exploit that allows the loading of custom FIRMs. The difference between it and A9LH is that it opens the system to much more that we could never do with A9LH like being able to modify OTP locked data and the use of self signed FIRMs. Also, SysNAND is the internal NAND of the console that the system runs from. EmuNAND is a 1:1 clone of your SysNAND that runs from a partition on your SD.