So if anybody is facing the same issue: Just select „IQaudio Pi-DAC+“. This works because this sound card is built the same way than the Pi-DAC Zero. Would be nice if the Max2Play Documentation would mention this. Also activiating this sound card in the IQaudIO menu or ins the „Raspberry settings“ did not make it selectable in the „Audioplayer“ menu out of the box. I had to ad the entry „dtoverlay=iqaudio-dacplus“ to the /boot/config.txt of the raspberry pi. After that, the sound card was selectable in the „Audioplayer“ menu.