FFT frequency question
Unlikely.  The top 6 FFT magnitudes would more probably contain several overtones or harmonics that are stronger than the 6 note pitches in a chord.  Furthermore, some of the spectral frequency peaks can be between FFT bins, depending on the length of the FFT.  So the frequency you've calculated by just multiplying by a bin index could be different from any pitch frequency in the audio.  Depending on any window used, you might also find windowing artifacts in the FFT magnitude spectrum.