Update time! I’ve been having a time and a half racking my brain trying to find a difference between NOS and OS modes. Hadn’t been able to at all. Was getting ready to chalk it up to my amp, the Jotunheim 2, just not being capable of showing me the difference…until I realized I had only been using it out of the balanced out. (For those of you that aren’t aware, the Jot2’s balanced and single-ended outs have different sounds, see WaveTheory’s review for a second opinion vouching for this.)
Plugged my Clear Mg into the single ended out, and heard the difference immediately. NOS is cleaner, instruments have more separation, and a slightly more forward. Cymbals are crisper and much more noticeable.
As to why I couldn’t notice that on the balanced out, I can only guess that it’s because the balanced out of the Jot2 already sounds like that, and that’s the best it can do . But since the SE out is smoother, warmer, and much more like the Asgard 3, the NOS mode of the Bf2/64 can clean it up and the Jot2 can show it to me. But that could just be me talking nonsense. Feel free to correct me if that’s the case, that’s just my guess on what’s happening. 
EDIT: Just realized I should probably point out that OS mode still has the qualities in my earlier post but it does sound more like the Bf2 than I gave it credit for at first.