Necro bump, had the G3 for a couple of months, and I can say hand on heart that I hate it for audio output from the headphone out...
It 'may' sound okay with sub-standard IEMs but, with better quality gear, to me it is thin and harsh sounding, pushing all but the most sedate of earphones into sibilance...
Glad to put this back down to just back-up duties - now have the Note 4
...will not comment on USB OTG for more than one reason - other than if you do that, then - yes, you'll get better results than from the headphone out, that is for sure...