Quick Answer: Audio is currently not supported in Liquid Notes.
Working with audio in Liquid NotesLiquid Notes is a multi-track harmony and melody editing tool for making complex changes to MIDI arrangements fast. This requires a harmonic analysis of the original music tracks as well as minute editing of the pitches of different tracks within your arrangement.
Supporting audio as additional layer introduces several technical difficulties which so far haven't been resolved.
Audio support may be added in a future version of Liquid Notes.