I have seen this SMT-C5320 behavior when the reverse path loss is too high. If you have not already, try connecting the Samsung SMT-C5320 at the location of the current working SA box.
You can also try to reduce the splitter loss to the locations serving the new Samsung boxes.
If you get the SMT-C5320 to boot you can check the return path loss by looking to see how hot the return data channel (RDC) is transmitting. Check levels by pressing and holding the "Info" and "Vol+" together for 10 seconds, then release. The diagnostic screen will appear after releasing the button
I have seen the SMT-C5320 Reverse Data Channel (i.e., OOB RDC) transmit levels as high as 57 dBmv on an operational box. When you get into the upper 50s transmit power level you are approaching the return path loss limit of these boxes.
In my case I was using a 2-way amplifier but neglected to consider the fact that a 2-way amplifier with a passive return path actually introduces loss to the return path (forcing the STB to transmit at higher level power levels in the reverse data channel). My solution was to replace the 2-way amp with passive return with a 2-way amp providing an active (amplified) return.