There has been some discussion using Golden Mean as a combination method for basic frequency combinations recently. Attached are some links that may be useful to you.
Not investigated the EEG frequencies here but we have seen a clear resonant frequency on HRV after 1h40 of meditation. The Peak of this frequency was at 0.094 Hz corresponding to a breathing rate at 5.7 cycles/min and a heart rate at exactly x10 more, so 57 bpm/min (spontaneous respiration). You can observe that ANS behaved like an oscillator in that case so it might be related to some brain frequencies as well...