Solve for -3 db Frequency Solve for Capacitor Value
Load Input Impedance (Ohms): 32
Capacitor Value (µF): 680
-3db Frequency (Hz):7.31
Optimal low frequency response (Hz):73.14

After some “study” I went for the 680uf caps. 
32 Ohms are the base impedance of my grados.
People say electrolytics color the sound, I must be deaf because I don’t notice coloration.