Hope it's not too late to reply. Using DAP to stack with DAC amp, DAP only act as a source in providing digital files. However, the quality of digital out does affect the sound quality and sound signature as well. So different players pairing with Mojo will actually give you different sound.

This is also the reason that you can find very expensive media players that people use in their HiFi system, mainly providing digital source only.

So far from my findings, players digital out is definitely better than hand phone (micro usb otg / iphone lightning)
In terms of player digital out quality, I would rank it this way. (best rank first)
1) Cayin N6 (provide most details and good separation. Sound is solid and could be aggressive to some) -coaxial
2) Sony ZX2 (It's comparable with N6, with softer and smoother sound, more musical and very easy to control)- WM port -micro usb
3)iBasso DX80, DX90, DX50 (iBasso player actually has very good digital out quality, except DX80 is a little bit warm sound. For those who likes cleaner sound may prefer X7 over DX80) -coaxial
4) Fiio X7 (Quite clean and it's android base and support music streaming. UI is not as fluent as ZX2 as a source)
5) Fiio X5, Cayin N5 - coaxial
6) Fiio X3II - coaxial

Haven't really tested out AK players hand to hand with the above players so no comment. Usually coaxial sound quality would be better than optical base on our experience (referring to the same device with both optical and coaxial) and it's easier for you to find a better quality coaxial cable.

Hope this helps. 

Anyway DAP feel like very bulky, if you bring out on both hand with DAP and Smart phone, btw you might do more with smart phone as well.

Recently I had tested with AK 100II the sound slightly better than iPhone 6s only, but when iPhone 6s plug in with mojo the sound totally was different a lot.

Maybe you can try it out, cause my currently setup with iPhone 6s or Mi Note with Mojo and RHA T20I the sound really impressive very different signatures. 

If wanna budget still can consider for Fiio DAC much cheaper to compare with chord mojo