I'm still unsure which is "ac coupled" and which is "dc coupled" I know the MSSH has no capacitor on it's input, so that makes it what, dc coupled?
no, the impedance of the 470uf cap remains the same (well not really, but i'm not going to do the math and dont know enough about the circuit to try), but the impedance at higher frequencies that can pass through the 0.22uf film cap is much lower and the path more linear. throwing randomly chosen bypass caps in parallel is very unlikely to improve matters. the frequency able to pass through a 0.22uf film cap into what? what impedance are your headphones? very low anyway; is likely to be up with the bats, so no wonder you didnt hear anything =)
I just calculated. The .22µf cuts off at 17khz with the SRH440 and 11khz with the Q701. It's high, but it should be audible on certain tracks. At least it didn't make things worse, so it can't hurt to bypass I suppose.