Unless you've already checked with Jon at Naiant, and not having a TB myself, I would definitely confirm with Jon that the phantom on your Tinybox is 12v. I could be wrong but I was under the impression that they could be made with several different voltage options. Measure twice and cut once, as they say.
With the B3's, therein lies one of the biggest drawbacks with those mics: they don't offer a pair matching service. Sure, they most likely will not be near-perfectly matched (like a set of DPA 4061's) but from what I understand the single mics are usually fairly close. Member illconditioned on these boards has considerable experience with B3's and has contributed a lot of information here regarding them. To the best of my memory, I don't recall him (or anyone else) mentioning a set of B3's so far off from each other that he couldn't get a good recording with them. That said, purchasing 3 single mics and coupling the closest two might be a prudent idea provided the dealer you got them from will accept returns.