Can't enable iPad in Audio Devices

Hi everybody,

I want to connect my mini iPad (Apple iPad mini, Wi-Fi Only/1st Gen)

via Lightning cable to my Mac.

Everything is fine, Mac trusted and iPad synchronized but in the Audio Devices list

the iPad is showing but grayed out, so I can't activate it:

So far I've tried to reset iPad-Mac connection several times without success,

I tried with my iPhone 5s the same and it worked perfectly (I could enable the device).

Are there any known incompatibilities between iPad models and this Apple feature?