I don't hear any harshness in the nbox recordings I've heard. YMMV.
Both solutions provide the Schoeps capsules with 60v and output in "line" level. With the PFA at +20db, they're functionally equivalent pieces of gear. You might be able to hear very subtle differences between the two over good headphones while doing a blind ABX test (I'd love to help make such a comp), but even if you could, I doubt you'd ever be really unhappy with the one you liked less.
A KCY Nbob> IPA is a little less inexpensive than a nbob> nbox set. But I'd make a decision based on the ergonomics of running your rig, your battery systems, and your downstream gear.
Sound wise? its likely to be a wash.