jagwap
1000+ Head-Fier
Do you know the max output current rating of opa1622 & 9218?
The OPA1622 is public domain, and it has more than enough for any headphone (130mA). It's the negative voltage rail that will probably give out first as that needs to come from an inverting buck or charge pump.
The ESS9218 datasheet is a little more illusive, but again it has a charge pump to deliver the negative rail.
Of course you could always couple the headphones via a capacitor, but that would be a dumb idea that iPods left behind at gen 5