I talked to RTB about putting content from MP10 to MP9, here's what he told me:
"They are a completely different format -- BNFM, which has no relation to either the Wii's MDL0 or the Wii U's BFMDL."
I don't know if this means I won't be able to pull this off, but I must not give up; I will put much time and effort to make MP10 files work in MP9.