When you say DSP are you referring to the EQ? I use EQ within moode. Happy with a slight bass boost on the HD800
It also has crossfeed and dynamic loudness equalization.
To me the ADI-2 DAC's big selling point is it's versatility. It can do fairly extensive DSP processing on its own, independent of your source, keeps separate settings for each output, and has 9 save slots for easily storing and loading all your settings.
If you only have one source, only use one pair of headphones, and can already do all the DSP you need in your source then you'll be leaving most the features behind. It's DAC and headamp measure better than the DX3, but that's not really something which is audible to a human ear.