I believe you are experiencing AVID's inability to import monophonic multi track files.
You probably need to interleave the multitracks into one polyphonic interleaved multitrack and it should import, I think.
If you have access to a PC laptop, there is BWF-O-Matic on BWFWidget, which can do this with your BWF files, and hopefully leave the originals intact.
If you are using a separate HD in FAT32 format,this is possible, I think.
I don't know what is available for MAC's.
Regards,
jim Rillie