What is the difference between control bus and link (what is Edge link?)

Edge Link:
Edge Link allows Edge series products to synchronise when powering up the units

Control Bus:
Jack sockets are used to send and receive power and volume commands from other connected Edge Series products.

There is no fixed, static switching voltage at the NQ trigger output.
The functionality only works with other Edge components, such as the Edge W power amplifier (as an example).
In other words, it is only compatible with the link input socket on another Edge product.
It is a low voltage encoded signal, not a static high voltage fixed level signal.
This is proprietary technology and will only work alongside other Edge series devices. It does not work like a standard trigger.