The Mojo can't function as a fixed dac as I read that its amp part is still engaged for line out. I am intrigued by your comment that it improves a few pieces as I am considering to get the MHA100 for desktop dac/amp. My Mojo is great with T5p but can't drive my new HD800s to my satisfaction.
Well it is not so surprising. IMO the DAC inside the MHA100 is not at the same level than the Amp. So an external DAC may improve on it.