If you have an existing scene with Unity Audio Source components, you will need to convert these Audio Sources to ASIO Audio Sources, represented by the CustomAsioAudioSource component.
To do this, go to AsioAudioUnity > Convert all Audio Sources in scene to Custom ASIO Audio Sources. This should convert all (active and inactive) Audio Sources from scene to CustomAsioAudioSource components, and automatically set the Output Channels.
To setup OSC for your ASIO Audio Sources, refer to Setup OSC Environment.