...As Dave asserts there is little going on in the surrounds and center...
Sorry I wasn't clearer in this regard.
Waveform analysts & meter-watchers won't see the surround / center/ lfe channels banging.
"Tame" rears & center, perhaps, but I hear plenty, not "little," going on. (YMMV)
Wonderfully balanced sound stage from my sweet spot for this drummer-less acoustic music.
I don't consider the mix "ambient" in the usual definition of "nothing in the rears but room & reverb."
I hear discrete elements in each rear channel wrapping around from a wide-panned location in the corresponding front.
Bluegrass pickers have an admirable but perhaps unusual to our heavily prog & rock-leaning crowd of laying back.
I mean, waay back. In this case, in the back speakers.
They are politely but solidly supporting the vocalist & soloists, until called on to take a chorus or three.
If you've ever been fortunate to see a live traditional bluegrass band like Del McCoury's, even in this age of unlimited microphones and mixer channels, they pooh-pooh that over-amplified rock-star nonsense.
They have no drummer or electric bass, they don't need to turn up be heard over them.
They stick a single old-fashioned 1930s Bing Crosby-looking omnidirectional microphone on a chest-high stand in front of the stage.
They adjust their picking intensity and choreography so every note is heard.
When called on to solo, the singer steps aside and the picker steps up to the mic.
The mandolin player has to get right on top of it, the naturally louder banjo or guitar, not so much.
Every player is listening to each other, and not in their Personal In Ear Monitors.
In other words, they do their own mix on the fly. In glorious MONO.
The front-of-house sound engineer has nothing to do but mind the master volume fader.