The traditional connection is the Arc connected to the TV via an ARC or eARC connection across HDMI. 

The Arc then generates a 5 GHz ‘hidden’ channel that the Amp and Sub(s) connect to. The router, however, maintains the DHCP information.  5 Ghz is purportedly used due to latency concerns, but it is much more susceptible to distance limiting factors such as dry wall, wood, and other materials, probably why Sonos uses a 2.4Ghz signal for most music connections.   Since, in a Home Theater context, all devices should be relatively close to each other, I suspect they were more comfortable using the 5 GHz channel, as they have with all their sound bars. 

I don’t believe I’ve ever seen an official post on it for the Arc, but I can’t see any reason why, if all devices are wired directly to the router with Ethernet cables, it shouldn’t work fine, it’s just not ‘as designed’. 

The Arc connects (ideally) to the Amp/Surrounds/Sub(s) over a 5Ghz ad-hoc wireless connection between the main player and those ‘bonded’ devices. It is often suggested/recommended that all HT devices should be in the same physical room for best connectivity.

All may be wired back to the main router/same switch, or the Amp may be cable daisy-chained via the main player back to the router, but personally speaking for HT purposes. I would recommend putting the Amp in the same physical room, rather than using a network closet, particularly if it is perhaps some distance away through walls etc.