I used a Chord Mojo with my Crack and even a Stereomour for a while. It sounded great. I ultimately preferred the Schiitt Bifrost Multibit, but not by a large margin.
Regarding voltage output of the Mojo, my understanding is that the 3V "line out" setting (pressing both volume buttons while turning it on) simply fixes the volume setting to give 3V out. There's a whole bunch of discussion about this on Head*fi - including responses from Rob Watts of Chord. To get 2V output, I believe you just bump the volume down 3 or 4 pushes - there's bunch of discussion online about this too.
Alternatively, I suppose you could set the Mojo to 3V out and pad the voltage down with some resistors. PB could probably help you with that. You could even build the resistors into a y-cable if you were inclined to build your Mojo-to-Crack cable.
But however you do it, I think you'll be pleased with the sound. The Mojo is very nice DAC.
Just my 2 cents, Derek