Grmia: Which resistor? One of us can compare with our IO's to tell you what the proper value is.
All: The reason "some hacks" sound good/bad depending on your volume setting is because of impedance matching.
is a thread that describes my mixed results with several hacks. To summarize, I built *both* hacks because I wanted to be able to run both headphones and external speakers. Complicating things was the fact that one of my headphones had an inline volume control, which would affect impedance.
All: Grmia's not the only one - I screwed up and tore off a few components the first time I did the audio hack. To prevent this kind of damage, I offer a few suggestions:
1) Be *extremely* gentle with things while you're building it.
2) When testing, you may want to "glue" the wires to the edge of the PCB before plugging in your test. That way, any stress goes to the wire and the edge of the PCB, not to the place where you've soldered to a component or trace.
3) AFTER testing, consider any glue you put over a wire and a surface-mount device to be "permanent". If you try to remove the glue, you may end up removing the device with it.
4) If you have to disconnect a wire, no matter how "loosely" you tacked it on with your soldering iron, use a soldering iron to desolder it. Do *not* "wiggle the wire until the solder joint breaks". Ever. You can get away with this on through-hole mounted parts, but it's suicide on surface-mount. Take the extra 10 seconds to desolder it properly. ("No, I've never done this and gotten stung, why do you ask?"