OK, I picked one these up yesterday as I was simply curious, and I now know I've reached endgame as far as headphone dacs and amps are concerned, but not for the reasons you might think.
I compared the Mojo against a Fiio E17 and a Steinberg UR22 audio interface using AKG Q702 headphones as they are the most difficult to drive in my collection. (I may repeat the experiment with the DT880 pro and the DT1770 Pro when I have more time)
And the results were that the UR22 (a $130 prosumer audio interface) demonstrated better control and tonality across the board with whatever I threw at it. Detailing was about the same, maybe the Mojo had the edge, but nothing that really stood out. Comparing the Mojo with the E17 I found that while the Mojo had better treble detail there really wasn't much in it otherwise.
Ok - so I'm deaf I hear you cry. Well that might be partly true as I'm pushing slowly towards 50 and suffer from mild intermittent tinnutis, but I'll also add that perhaps I don't look for the same things in music as some of you guys, and this has set me thinking about what I actually do look for in music that's different from an audiophiles perspective.
I've come to the conclusion I look for an overall balanced tonality that gives me the music. I don't look for minute details or accuracy of positioning as these things in truth don't really matter to me. As far as soundstage is concerned I simply don't hear that through headphones at all, not even with binaural recordings - in fact they just sound like a phasey screwed up mess to my ears.
One thing I've found that might help you understand my position is that I've had the pleasure of listening to some really high end headphones and the truth is is that the higher up I go the less I actually enjoy listening to them. i've often played off the HD800 against the DT880 and the truth is that I'd take the DT880 over the HD800 any day. Sure the HD800 is clear and precise, but the DT880 has more meat and sounds more natural and enjoyable to my ears, whereas the HD800 sounds, well, artificial. - Basically I prefer the tonality of the DT880.
I'm not dissing the Mojo in anyway or form - it turns on, connects to my Mac straight away and delivers a good clear signal to my HPs - it does what is says on the box. The fact that I'm not hearing any night and day difference is probably down to how I approach listening to music - I simply don't listen for the things that make the night and day difference to other people.
What might surprise you is that I'm not disappointed at all. It's confirmed to me what I've long suspected in that I just don't hear in an "audiophile" way. As for being 600 bucks lighter, well I'm taking the attitude that it's a cheap price to pay to know that I'm at endgame (It could have cost a hell of lot more), at least as far as DACs and Amps are concerned.
As for the Mojo, well I'll hang on to it as I need something that will connect to my iToys when I need to use demanding HPs, and it seems to be a perfectly competent DAC plus Amp.