djay 2 + ipad + alesis io dock = pre-cueing very low

I’m using my Alesis iO Dock as a sound card for P10 connection to the main PA, working great.

But when I plug in my headphones throu the iPad P2 jack the pre-cueing sound is extremely low, nearly inaudible in not-so-noisy situations.

When I take the iPad out of the dock the main volume coming out of the headphone jack works great but as a pre-cueing it’s useless.

Is there any way I could fix it? (I got a headphone amplifier but it didn’t help at all)

Thanks in advance.