I think i have the same problem. I split the signal with a lighting - p2 female cable, then split it into Y cable p2 (2x)P10: I link the right channel of my iphone direct into my PA and the left channel to my headphones amp. The issue i get is that on my headphones instead of hearing the first 4 metronome beats (so the backing track will start to play) i can only hear 3 beats. But the funny thing about it is that on the first song i can hear all 4 beats, then on the following songs songs it always keep muting the first metronome beat.