Can anybody please tell me if there is a difference between NVR model numbers DS-7616NXI-I2/16P/4S versus DS-7616NXI-I2/16P/S? The only difference seems to be the "4" before the S at the very end. Basically I'm wondering whether I can update the firmware on my DS-7616NXI-I2/16P/4S using the...