I found a nugget in 400 documentation to add to my thread:
"Reception functions will be used on the 6873 and if required, the PKM module(s)
• When every MiVO 400 Hospitality base bundle has one 6873 set and one PKM module
• Operator Console keys are used for call handling (internal dial 0 and external inbound answer point)
• Operator console keys can be programming on the 6873 & 6869 only
Note: When a 6873 and PKM are using PoE, remember that this requires Class 3 power. This combo will require 12.24 watts,
worst case. Please review the Mitel IP Set Engineering Guidelines V2.2 for all things sets.
Note: If using Streamline, one port can only provide 10 watts max. Please review the Stream Data Sheet"
It sounds like a power brick will be needed for the 6873/PKM combo.