Yeah, ok. I see your points but looking at it from the other side - If your preamp had an impedance change option you'd use it, almost certainly, right?
You'd learn that you like your
sm57 better on setting A and your NT1a better on setting B?
So if you're DIY handy and interested, what's really different about making an XLR barrel to do the same job.
I'm only intrigued by this thread because I've hated my re20 for years (on my voice) and never used it, and recently discovered that what I hate is the sound of the re20 through one particular preamp.
Now, this is a very clean high gain low noise preamp - I'm not hearing 'character'..... It has no identifying tone that I'm aware of, but I can tell you from a mile away which pre the re20 is plugged into.
Through preamp A you'd swear someone had eqd a very tight boost around 1.5k, whereas through another (equally clean) preamp the re20 sounds great.
Now, the re20 is known and recognised - A lot of people want
that sound, so now I'm wondering if I should be investigating mic and input impedance.