I'll also add:
Coupling capacitors on headphone outputs must be no smaller than 470µF. (Going higher still doesn't hurt, but will take up extra PCB area for no noticeable gain. Well, audio coupling capacitors in general should be sized to keep the −3dB frequency at least an octave below the lowest frequency of interest, but it's rare for them to be undersized on inputs or [non-headphone] line-level outputs.)