You should only need to update your DSP to 1.2 first, the 1.3 "CPU" update includes all the cumulative updates from the previous CPU firmware.
"Please note that this Upgrade (CPU version 1.3) should be used with DSP version 1.2. Some features may not work properly if an earlier DSP version is used with CPU version 1.3."
"Should you want to go back to the older CPU or DSP Firmware these files may be available on the GRE America website. Per above, version 1.2 or 1.3 of the CPU requires DSP version 1.2 for all features to operate properly. If you revert to an older version, please change both the CPU and the DSP to the older version."