Actually, it would be a great fit for acoustica. The DXII excels with any good recording of natural instruments and vocals. Is it possible to get some sibilance occasionally? Sure. But that's par for the course when it comes any W signature, and is largely going to be recording-dependent in many cases.
I absolutely adore the Stage 3, and recommend it often. To me, I think a good 80% to 85% of Head-Fiers looking for a great IEM can just stop at the Stage 3 and save much money - not to mention weeping and gnashing of teeth from - having to search further. In the grand scheme of IEM things, it's wonderfully affordable for the level of performance that it offers. Having said that...
I'd take the DXII over the Stage 3 if the budget allows. It's just a bit better all around, especially in terms of clarity, and that sense of air and space up top. I'm not saying we'd hear a whole lot of fundamentals up top... but the DXII seems to have an infinite taper in the highs, without out a roll-off that sounds like there's an annoyingly intangible boundary. And that little thing, on top of the wonderfully pleasing bass and articulate mids, ugh, it's such a nice cherry on top.
Now, if budget is no issue whatsoever, then Kublai Khan. Think of the DXII and Stage 3 as a series of very tastefully done compromises on what the Kublai Khan offers... endless extension at both ends, with bass/mids/upper mids crossed over to near perfection in between.
But back to the original point, if a very well done low end is what you're looking for from Noble's line-up, I stand by my Spartacus recommendation - with the caveat that I haven't heard the Onyx yet.