what I am trying to understand is if the original recording is with
euphonic distortions that are deemed as positive then don't we want the
most transparent system to hear the original and How does tube
euphonic distortions add a stage to the sound?
I wouldn't worry about the original recording! Some are great and some are terrible. The way distortions occur and how some are added in the studio causes things to work out differently. When you are playing back you simply want the most transparent you can get but without the playback editorializing on the content.
By this I mean the playback apparatus has to be well-behaved. I've seen some systems sound great with a great recording and then freak out when a poor recording is played. But get that same poor recording on a properly set up system and while it won't sound great, at least the playback won't exacerbate problems.
That is one reason I eschew brightness and harshness in the playback as it will make bad recordings worse. It sucks when a favorite artist has a lousy recording; it sucks worse when your system can't be graceful about it.
With regards to sound stage, it appears that a prominent 2nd or 3rd harmonic somehow helps the ear winnow out detail in the recording. I do not know why this is the case so I'm going on a lot of anecdote (and familiarity with recordings I've made on location and in the studio), but I did encounter one paper where the experiment was to add a 2nd harmonic to the playback and improved soundstage was the result. I think more research is needed. At any rate in my own work it appears that the *amount* of distortion isn't the point- but what is important is that even if the distortion is super low, most of it should be the lower orders.
