iPhone mic input and OpenAL sound playback

sorry for coming up with this again, but as it is iPhone related, this forum might be more relevant:

I want to use the microphone input just for level detection to trigger
short sound files. It’s mainly to obtain the shortest latency possible.
I’m not routing the microphone to the speaker by

ofSoundStreamSetup(0, 1, this, sampleRate, initialBufferSize, 4);

That portion works.

But if I add a SoundPlayer in the testApp.h, it’s initialization seems to
cut the microphone all together:

ofxALSoundPlayer synth[10];

Where can I set the AVAudioSessionCategoryPlayAndRecord like I would
in Object-C?

Any example is very welcome

Thanks, Hans