The midi used by the 2box is weird and to this day I haven't got a clear answer from them as to why is it like that, but I use the SD3 2box mapping that even has two, one for the drumit 5 and one for the drumit 3 and it works perfectly, but there is one detail almost no one knows regarding the hihat part of it: make sure the PED setting in the Unit-MIDI page is set to CC4â–¼!, which sends data continuously and works better for the SD3 hihat.
By default is set to something else, I can't remember, but just set it to the above value and you'll be fine.