Did you put a fiber optic extension cable in .
The Sos system is on the most bus . I believe people mentioned
that they needed a fiber optic extension in the head relocation thread
to get the SOS error to go away.
The SOS and bluetooth modules are on the Most Bus ring along
with the L7 amp if you started with and L7 system.
If you started out with an L7 system there is no wiring to the speakers from the Head Unit only a fiber optic cable.