Very strange. I can clearly hear a difference between X3 and Clip+. But I have changed the opamp, so I cannot compare stock X3 to Clip+. I also have RE262, SM3 (and Brainwavz B2 instead of DBA-02). The soundstage from the Clip+ is not as deep and resolution is lacking. Have you tried intense listening to the Hi-res demo tracks? You can re-encode them with foobar to 16-48 so you can play them on Clip+ as well.
My resolution test track: Rebecca Pidgeon with Spanish Harlem.
And on the Chesky demo CD I find the very first track to be quite revealing as well.