It seems like the bop to bvh conversion is possible, but it requires some extensive work in 3Ds Max and several steps before user manages to get the final file. You can find more about this subjects for example in this forum entry.
Convert Character Studio biped file to Biovision Hierarchy Animation file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert bip to bvh on Windows
A widely-used 3D animation application from Autodesk
Convert from bip file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.