I just received my DP-X1 from Moon Audio (it has CD in the serial no so I assume it was for US market).
Using the balanced out (with two different cables) I am getting a lot of distortion in the left channel. Is this the issue with poorly built sockets or some other bug?
Note: I am using the stock player that came with the DAP and have not installed any apps myself. I also put it in airplane mode to avoid any interference.
Don't know if you, or anyone else knows this, but the issue you described is something Onkyo kinda are aware of but it is usually user error (in many of the RMA issues they have received outside of poor jack sockets):
Never,
ever plug both single-ended (unbalanced)
AND balanced jacks simultaneously, set the player to either balanced BTL, or worse ACG, and press play.
This actually actively damages the internal amplifier circuitry.
Many noise issues via amps is related to damaged amplifiers, from what I understand to be, a shorting of the internal electronics or something similar.
The above is advised in the balanced menu and manual.
Of course, I cannot say if this is something you may have done or not, but contact Moon Audio immediately for help and possible replacement.
There might be other reasons too but I'm basing my info on direct feedback from Onkyo JP and Onkyo UK itself.