Any RCA ports are analog, and not digital. Your PC would be converting from digital to analog, then the Port would be converting from analog to digital and sending that signal to the speakers. 

Thank you for your reply, Airgetlam,

I slightly modified my original post to make sure that I added my Port to my not-Sonos analog amplifier and old non-Sonos speakers.

SONOS can directly play files stored on the NAS, no computer is required in the signal path. SONOS controllers, phone/pad/computer are simply remote controls, no music from the NAS passes through the controllers. Once music play has started you can shut down the controllers. If you are using a streaming service hosted by the phone/pad/computer, then there may be extra format conversions. In the case of PORT playing from the NAS or directly from a streaming service,, the PORT’s DAC is used only for its analog Line-Out.

Let me clarify by my quick and dirty diagrams.  Currently my connection is “Case 1”.  My goal is “Case 3” without any Mac, but I will have to invest in some time and money to set up a NAS.  So I’m curious if there is any sense to connect like Case 2?  My original question was about apparent double DAC’s in Case 2 since Sonos Port has an internal DAC.

Port can be wirelessly pointed to the music in the Mac, and after a D to A conversion, supply it to the Non Sonos Amp via RCA. Even in Case 1. 

By moving the music to a NAS as in Case 3, what is achieved is removing the Mac from the music play loop, with Port pointed directly to the music on the NAS.

The external DAC is then redundant in all cases.

In terms of audio quality, there is no difference between computer, NAS, or USB storage of the files. A string of multiple ADC and DAC conversions risks audio complications. I don’t have any music stored on my computer. I prefer using my NAS because I can take the computer down for maintenance and the music continues to play. Also, I’m very impatient and music playing from files stored on the computer slows the computer somewhat.

Yes, the external DAC is redundant in Case 3.  But I don’t know how to omit the External DAC in Case 1.  Can Port directly access music files in HDD which is connected to Mac via USB?  If it really does, it is a great news to me, but I do not see how to make that happen!

I quite agree with you that my Case 3 is the best, where Port accesses music files in NAS and does not need a computer.

If the Mac and Port are on the same WiFi network, Port can see the wired to Mac HDD, the music files on the HDD and play music from it, via WiFI. Exactly as it would in case 3, where the NAS is directly connected to the network.

Great! I’ll try that as soon as I get home.  I’m on a trip now.

Since I have not used it for a long time, I am not sure what settings need to be set for the Mac where the HDD wired to it is to serve as the NAS; the Mac may need to not sleep as long as music play is needed. 

SONOS can directly play lines stored on the NAS, no computer is needed in the signal path. SONOS regulators, phone/ pad/ computer are simply remote controls, no music from the NAS passes through the regulators. In terms of audio quality, there's no difference between computer, NAS, or USB storehouse of the lines. A string of multiple ADC and DAC transformations risks audio complications. I do n’t have any music stored on my computer. I prefer using my NAS because I can take the computer down for conservation and the music continues to play. *

*Moderator Note: Modified in accordance with the Community Code of Conduct.*