Hi @sixerdoodle - great project! From your webpage:
Right now, the next two bytes are a bit of mystery. On my system they are always 0x91 followed by 0xC7. Always. Not sure what they mean since they never change.
From your description, it sounds like you have a first generation DSC PowerSeries panel - these supported up to 2 partitions and the 0x05 command uses 2 bytes to display the status lights and a status message for each partition - so those two mystery bytes are for partition 2. I've been interpreting the 0xC7 as a partition disabled message, but DSC probably has some other official term for it.
If it's useful, I have much of the protocol decoded at taligentx/dscKeybusInterface in src/dscKeybusPrintData.cpp (see the develop branch for the most updated decoding).