Last week I heard Osmo Vänskä conduct M6 with the Minnesota Orchestra. I was surprised that the sound was dull and murky; I was in the tenth row and have sat near there for several other concerts; on those occasions the sound was much clearer. The upper woodwinds were really buried in the texture, with many usually audible details lost.
Vänskä used S-A ordering. Tempo for the first movement was a touch slower than what we might call the consensus. I thought the performance felt generic and lacking in feel for Mahler's rhetoric early on, but that it did improve. Passages that should be pianissimo never seemed to go below mezzo forte, robbing the alpine heights episode of its ethereal beauty.
The hammer in the finale was a huge wooden mallet, our percussionist adding an air of theatricality as he raised it to strike. The instrument was impressively loud, but produced a sharp report at odds with Mahler's instructions ("short, dull, powerful, not metallic, like the stroke of an axe"). For the second instance, Mahler specifies cymbals and tamtam "only if the hammer is not sufficiently penetrating." Officially the extra percussion should have been omitted but Vänskä included them, as most conductors do. Toward the end, just before the (omitted) third hammerstroke, the tamtam is marked forte but was definitely played fortissimo. Nobody likes a loud gong more than I do, except of course Barry, but I like to assume Mahler knew what he was doing.
I have a number of Vänskä's BIS recordings, and to my ears they maintain a high standard of both artistry and engineering. I suspect that Mahler is relatively unfamiliar to both conductor and orchestra, and that both need more experience to obtain more idiomatic results, particularly with as large an orchestra as in M6.