These drop down lists allow to select audio input and output devices from the lists of available devices. By default Wave Mapper is selected for both input and output.
Audio Output allows to select an output audio device.
MIDI Input selects the device to use for MIDI Recording function. MIDI Recording is available in TrueTone Editor, see the Playback toolbar.
MIDI Output allows to select MIDI out device to playback MIDI notes.
Never Send "Program Change" Command to MIDI Devices may be useful when using some external MIDI synthesizers. This settings blocks all Program Change messages when playing any MIDI data, preventing any instrument changes. In most cases you do not need this control.