The connection type of the agk701 is not 1/8 inch. It's 1/4 inch aka quarter inch. It comes with an adapter for 1/8 but that is not it's native plug type.
A headphone amp is also recomended. A 1/4 inch one. Also you might want to look into getting a flex adapter instead of using the hard 1/8 adapter it comes with. Ever see a trs output sink into itself? I have.