Over on the Head-fi Chord Mojo Official Thread I had the answer from two of the Chord engineers about 2V rms.
Here from Rob Watts (Mojo designer) post 8201 on page 547.
http://www.head-fi.org/t/784602/chord-mojo-the-official-thread-please-re...
He said, quote, "Yes 4 clicks down will set it too 1.9v (both balls indigo). Each step is always a 1 dB change".
In other words start the Mojo. Within two seconds press both volume buttons. That sets it to 3V rms. Click down volume four clicks and it will be at 2V rms.
Mojo Ideas, real name John Franks (another Chord engineer on the Head-fi forum) made post 8231 on page 549. He answered set it to about double blue, meaning the colour the volume buttons are at specific voltage setting.
Difinitive answer then.
I am so tempted to go ahead and open the Mojo now.