John…
Anything you do on a channel will carry over to any and all buses to which the channel is assigned UNLESS you select a signal pick-off point for that bus which is pre- the process. This is clearly detailed in the manual, I believe, and is channel processing.
See section 9.9 “Mix Routing” in the manual regarding pick-off points for channel>mix sends.
Bus processing is just that and will apply equally to and across all channels assigned to the bus. Any EQ, compression, etc applied to the bus covers and affects all assigned channels but will be peculiar to that bus only, with the exception of buse in sequence such as group>mains where the group processing carries forward to the mains.
I suspect this linear carry-over also applies to matrices, but I only have a Qu-16.