AudioDevice=ALAudio.ALAudioSubsystem

and add:
[ALAudio.ALAudioSubsystem]
ALDevices=OpenALSoft
DopplerFactor=0.010000
UseOriginalUnreal=True
SoundVolume=200
UseReverb=True
EmulateOldReverb=True
OldReverbIntensity=1.000000
AmbientFactor=0.700000
MusicVolume=130
MusicPanSeparation=70
Channels=64
OutputRate=44100Hz
UseDigitalMusic=True
bSoundAttenuate=False
ProbeDevicesOnly=False