Biophysics has several branches, and I don't know how gravitational waves (which essentially has to do with quantum field theory and general relativity) can directly connect to the field. However...
1) Protein folding and macromolecular structure and dynamics, which has traditionally been the dominant field in biophysics, requires a lot of similiar mathematics (i.e. basic analysis, diffeq). In specific, people are starting to use path integral from QFT approach in solving the protein folding problem
2) In neurophysiology, which can be roughly considered a intersection between biophysics and neuroscience, many of the same mathematics is used (the math for Zeeman's effect in quantum mechanics is used for predicting visual hallucination, for instance)
In general, biophysics has more to do with condensed matter physics (crystals, solids, fluids) than high energy physics or cosmology. However, if you are strong in hard physics, it's pretty easy to make the transition.