The perils of duplicated threads…
The iMac and the Nucleus would both be on the network. The P6 would be connected by USB to the Nucleus. It’s an option.
Regarding the coax and USB, I concur with @Boris_Molodyi as already said on the other thread:
I’m aware that USB was never intended to carry audio; so am determined to get something better.
Roon recommends using a networked streamer.
If using a direct connection, there’s nothing that’s better in any meaningful way than a well implemented USB interface.
It’s true that USB wasn’t designed to carry audio because there is no audio to carry at this stage. It’s carrying digital data, which really is nothing but a long string of very large numbers. Audio only comes into play at the analog side of the DAC, which is well isolated in any competent design.
You can’t connect the P6 to the Nucleus by Coax because the Nucleus doesn’t have a Coax output. But there’s no reason why you would want to.