Yeah, I know what you mean that I may be hearing the differences between the quality of the capacitor components more than the effect of the capacitance value change. I did switch headphones from the Bose Triports (which has a strong bass output) to my Senheiser HD600 which has a less emphasis in the bass and it sounds much more balanced.
I used to design and build high end speaker systems and crossover networks years ago... I know on paper and equations and graphing responses using software shows minor slopes and response changes on paper, but I tell you they make a big audible difference (even a .1 ohm resistor) put in place on a crossover network would be enough to attenuate a spectrum to hear a marked difference when A/B'ing them. It is just not the one frequency you are attempting to attenuate or un-anttenuate that will change, it is the entire frequency spectrum of energy that changes shape along with the value change (no matter how small it may seem on calculations). It changes the character of the sound. Anyway, I did/do hear a difference ever so slightly in favor of less heavy bass with the 10uf capcitor I really believe. BTW, even though I said it was Radio Shack capacitors, the caps are made by Xicon. I don't think they are that bad for electrolytics (which I prefer sometimes over the more exotic audiophile grade polyester/polystyrene/metalized, whatever caps that sometimes sound too sharp and bright). I realise also here that we are speaking about low level voltage and higher impedances here when dealing with these low level preamp signals versus high current higher voltage speaker (power amp level) lower impedance realm, but my point is I think it makes a difference. Thanks!