[JeffreyAK]

Can't speak to the Emerald specifically, but I mess with the sub-bass tuning fairly often on my S12, and certainly within the +/- two semi-tone range (per string) it seems fine. Probably, a carbon-fiber guitar won't care. Generally, I'm tuned down with less tension than standard because the low string on the fretted neck is D, not E, so my highest harp string is C or even B, and it goes down from there.

Playing live, I don't know, perhaps that's where a pickup would come in handy, but for recording I mic the guitar with two mics. It's the usual guitar mic problem, where do you put the mics, but more complicated since the top on a harp guitar is very large and you have more than one hole. I've messed around a bit with the pickups on my Tonedevils, they are uninspiring but no better or worse than the pickup on my Taylor, and no match for a good mic.