You left the 2 * pi out of your formula, but must have used in in your calculation. I would think this should be sufficient. On my recent coupling cap experiment in my preamp, I had used a 1uf on the output, given the 1M resistor to ground. Of course I forgot to account for the amp input impedance in parallel (10k), so the 1uf gave me ~14Hz... definite rolloff that I could hear. Went back to an 8uf cap as the stock one had been. No rolloff that I can detect by ear now, and RMAA looks much better.