For me personally, I don’t use multi-source same system settings for doing any referencing.
This was a big issue back in the Tape Vinyl source days, and was one of the major reasons Equalizers were used. It never really worked, using preamp sections with multi-sources but we always had frequency adjusting tools to somewhat help, but it never really was a purist approach. In reality to have a true discrete system you would only have one source, or even one input, for the system. HEA tried to bend the rules on that one, but that’s not being discrete.
You know, saying systems that only have one volume control with several inputs is being discrete is a bit of a scam. Saying one volume control is discrete period, is a scam when you think about it.
MG