How can a system be judged with highly processed, non acoustic music?

If you care about how vocals sound, you care about acoustic music.

One of my go-to tests for fidelity is whether I can discern the brand of acoustic guitar(s) being played. Gibsons and Martins sound very different in real life. Other quality brands occupy the middle ground between them. 

@wolf_garcia. Yeah, stereotyping guitar brands with a particular type of sound is ultimately treacherous as hell, but I still can't help but do it. I also gotta say that me and the wife have more than our share of steel string acoustics in the house.  Damn, her Everett sounds lovely! And in earlier days I spent an inordinate amount of time at McCabe's Guitar Shop and similar joints, taking guitars off the wall to sample.

At any rate, I think of a Gibson acoustic as sounding dry and midrangey --  a sound particularly designed not to get in the way of vocals. A Gibson L-00 (yeah, it's tiny) suits this sound to a T, as do many Gibby dreads. Martins, particularly dreadnaughts, sound big and complex -- made for propelling bluegrass bands. 

I've never heard or played an Olson Guitar, but I've played the other brands you mention, and sound-wise they all generally hew to the Martin sound. And  oh yes, I truly love the Froggy Bottom and the Santa Cruz.

@mglik -- I gotta tell ya' that pianos' sounds can vary remarkably by both brand and size. Again, I'm typecasting here to beat the band, but Steinways tend to sound clangy and Baldwins tend to sound mellow. Bosendorfer inhabits the tonal spot between them.

mglik
How can I forget Fazioli? I actually played one at one of the piano stores I used to haunt. (Yeah, is this refrain getting old. I'm a more of a sucker for musical Instrument stores than stereo stores.) I think Maurizio Pollini was playing a Fazioli when I saw him live.

And oh yeah. I sweet-talked a 1930's  L-00 out the owner's hands at an Old Time jam. He said it had spent WWII aboard a Navy ship. I was loathe to admit to him that it sounded a ways better than my brand new Ren Ferguson-built edition...my current fave among my gits.  

frogman -- Hey, thanks for the comparison vid. Routed it through the old hi-fi. As for making a choice among the three makes, all three axes offer up equivalent versions of the truth. The Bosendorfer gives me a just a little bit more power. The Fazioli a bit more sparkle & presence. The Steinway a bit more old-fashioned seriousness & comfort, i.e., the sense that this is what the classic/romantic composers probably actually heard when they composed.

I gotta say, though, that the YouTube was the proverbial beotch to get through. Each time I'd put it on, several minutes through it'd be hijacked by a different, abjectly inferior Piano YouTube that could not be gotten rid of. Eventually I was able to hear all three pianos go through their paces, but what a headache! It made me nostalgic for the time when, in L.A., I'd just get in the car and brave the traffic to different piano emporia.

frogman -- I'll bet my memory is playing tricks on me, but I'm pretty sure that when I went to L.A.'s piano shops and played those three brands brands, it was only the Fazioli that gave me the shakes. It was only the Fazioli that compelled me to return to the dealer and drive them nuts with my horrible playing, once again.

I might want to say, too, that for a while I lived within walking distance of a very good piano store. And that I continue to love the early 20th Century, 52" Mason & Hamlin upright. I was compelled to buy it when the wife lost patience with the living room hogging Petrof Grand I'd been banging on previously.