For burning in headphones, playing pink noise on a continuous loop is best. But for burning in DAP, playing anything will do. Just turn it onto High Gain, and use the balanced port. That way you're activating all the amp chips.
I can understand you preferring the Mojo. A standalone DAC, even a portable one, is almost always going to be better than a music player. And Chord makes some of the best DACs on earth. Even a top of the line DAP isn't likely to beat it.
DAPs are about sacrifice. Even when you spend upwards of $1,000, you are sacrificing a certain amount of audio quality for portability. That's just the physics of our reality. Look at the size of the Mojo, and then realize, that's not a music player. All it is is the DAC part. How much bigger would it be if you incorporated a CPU and its accompanied circuitry, storage capacity, display, all the required components to support the Android OS, etc... Well, how much bigger is it when you attach a smartphone to it?
The Cayin N5II is not meant to compete with a standalone DAC of Mojo's caliber. It's simply a really awesome alternative to stacking. If you want to get close to Mojo's quality (and I've not heard Mojo, so don't take this as absolute truth) you will need to invest in something far more expensive, like the Opus#2. Of course, that's even more an Mojo. But again, you are paying for quality shrunk down in size. A sacrifice to do away with the hassle of stacking.
Such is life.