Wavebank (.xwb) and soundbank (.xsb) files are generated by the XACT GUI from a project file (.xap). The XACT GUI cannot load the generated files, it can only load .xap files.
The binary format of the wavebank file is documented in the header xact2wb.h. Using this header, you can write a tool to parse data from the wavebank.
The binary format of the soundbank file is not documented.