Room Nucleus+ vs what for dCS

It seems like for networked listening, as long as the device can serve up the file quickly, there shouldn’t be a sonic advantage to other devices

...What I’m trying to understand is if there really is any sonic difference between them if running over Ethernet

There is, as in capital IS. Pursue different options to find out for yourself.

and the core is not located near the rack.

The Roon Core Component can most certainly be near, or in, or on the rack. Consider it an audio component and treat it as you would any other audio component in your primary system.

No reason to use WiFi. House is wired and WiFi will always be inconsistent due to interference and overlapping zones.

Not true. WiFi can be used to effectively isolate the 'dirtier' sections from the more important and hopefully 'cleaner' sections for audio applications. There are other reasons as well. Dig deeper as WiFi can be your friend.

@audiotroy 's posts above are valid and share important and helpful information.

I have been evaluating DACs and dCS is on my list. I’ve auditioned the Bartok, the Rossini, and a full Vivaldi stack. I’ve also heard the Rossini in a neighbor’s system and have heard dCS products elsewhere. My most recent auditions, both at the dealer and at my neighbor’s home, coincidently / by happenstance were both fronted by a Roon Nucleus.

Based on what I am hearing you express, the dealer’s choices, and what my neighbor ended up with (in all cases... the Roon Nucleus) I’m fairly sure that dCS as well as their dealers believe that dCS is impervious to the ethernet signal being sent it’s way.

Once a position gets dug, it tends to stick / stay and is amplified by those that follow the manufacturer / dealer guidance.

I happen to disagree.

I’m running a dCS Debussy DAC, Roon Core on a sonicTransport i5 and streaming files from a Synology NAS to a DCS Network Bridge.  The network bridge doesn’t support USB out so I use dual AES/EBU cables to the DAC.  Dual cables allows me to listen to DSD 128 files.