In the X7SBi manual, it says the DIMM sizes supported is up to 4GB, but the total memory supported is 8GB. Since this is a 4-slot board, please kindly confirm whether it can take four 4GB DIMMs to populate 16GB of memory?
It's the limitation of the Intel chipset. It can only support up to 8GB of memory in total, and will see the maximum of 8GB only. This is confirmed.