Regarding the XLR Yggdrasil output to RCA singled-ended input cable question, Schiit has passed on more specific information to Pete at Triode Wire Labs who is very kindly making up the needed cables.
Yes, Schiit does recommend "matching the input impedance of your device input with the resistor."
Schiit even provided a circuit diagram which I apparently can't post because I'm too new here? Here's a link to the diagram instead; maybe someone who knows how to embed the image can post it if interested.https://imgur.com/tU41PcH
All of the above is likely accomplishing the same purpose as the 600Ω transformer. I hope this helps.