Agree with @pesky_wabbit
"generally, whatever is at hand, they tend to have an ability to hear through the shortcomings of very ordinary systems explain nuances in performances that most people would fail to detect"
I’m pretty sure most committed musicians learn early on to simply take all their musical cues from life, not the recording. For them, that’s the wellspring of its creation: the sheer, in-person Sound of it...live sound from live instruments...I don’t think it could be any other way for them really - in their work they always have to consider how their music sounds live first. No point in relying on a facsimile to recreate the real thing when you’ve already got the real thing.
So when they’re listening to a rig, for them practically speaking it’s not much more than a placeholder, an index, but in their own heads it’s their musical ’memory’ of a live event or sound that’s being accessed. They might think of the rig as more just a useful tool for composition than for appreciation I think.
Again, in their work, it’s their associative memory of live musical sound itself that is their primary stock in trade.
The musicians are the flip side of the audiophile experience. The pro guys are the go-between.