I can't find anything that looks like a root key anywhere. I'm not quite sure what Prev/PrevSec mean, the order is though in-file: 1) Prev 2) Normal 3) PrevSec
They're in triplicate so must be related, perhaps as you said.
It looks like root key is now supported, but it's a floating point. 1.0 = 78, 38 = .5 and 0 = 0.0, I think. Maybe someone can test. I support importing the three sounds now.