Ion-beam sputter-deposited alloy films of Co74Fe6B15Si5 and Fe75Ni5B15Si5 were examined for their magnetic and structural properties. Films were characterized by ferromagnetic resonance, vibrating sample magnetometry, and extended X-ray absorption fine structure (EXAFS) analysis. Using atomic parameters deduced from EXAFS modeling and fitting procedures, magnetic properties were calculated with no adjustable parameters. Correlation between perpendicular FMR measurements and EXAFS first-shell modeling suggests a low-temperature formation of cobalt-borides in the Co74Fe6B15Si5 alloy. Annealed Fe75Ni5B15Si5 samples did not display evidence of structural and/or magnetic instabilities until the onset of long-range crystallization near Tann=400 degrees C.