Complex sentence: Some multitrack software also provides MIDI playback functions not just for audio; during playback the MIDI data is sent to a softsynth or virtual instrument (e.g., VSTi) which converts the data to audio sound.
Split into simpler sentences: Some multitrack software also provides MIDI playback functions not just for audio. For playback the data is sent to a softsynth or virtual instrument (e.g., VSTi) which converts the data to audio sound.