WaveFront based synthesizers are currently the Maui, Tropez, Rio and Monterey.
.WFB files contains a whole MIDI Bank, .WFP a single Program and .WFD a complete drum set.
Instruments using ROM samples, of course, can't be converted.
If the files doesn't use embedded waveforms, but external .WAV files instead, you must have the .WAV files in either the exact path they where when the .WF? file was created, or, in the same directory as the WF? file.