Here are the pictures:
http://imgur.com/a/fwzkC
I know I've done a terrible job at soldering the caps and I probably should have let someone else do that for me. It look very ugly but I've checked the solder points with a multimeter for continuity and they're all ok so that shouldn't be the problem.
One thing I've noticed is that according to the schematics, pin 1 and 7 on the op-amp (U15) should be directly connected to the caps behind the audio connectors. I checked if they are with my multimeter and pin 1 (bottom left corner of U15 on the first picture) is not (and pin 7 is). So I guess that could be the problem but I can't really track the trace in between.