Maybe you should emphasize that you have the upgraded adapters recommended (by the designer) for power-hungry headphones (that others such as JDSLabs do not provide).
Or consider selling them separately, if that would help? Probably not, if you want to get rid of both. Possibly also just take a larger price hit and reduce the price, as most people prefer options from other sources unless there is a significant discount to be had via sale/trade forums. Do threads usually get that many views without any action? I think it's the price, really. For example, Mayflower Electronics offers O2 + ODAC combo in one box for $250 shipped.
You might as well list what the gains are, as the build doesn't look standard (different faceplate than some are used to). Maybe offer to change them if you have different resistors handy.
Good luck selling them.