Why do I need to use a DAW?

Soft Arranger on its own doesn’t produce audio, only MIDI. You can think of it like a sequencer. The MIDI data it produces needs to be sent to some kind of sound generator so that you can hear the music. It could be a hardware synthesizer or some sort of software synth/sampler. 

To be able to sound as consistent as possible across different computers I have decided to go with several instances of a VST sampler (TX16Wx) which are hosted inside the DAW (Reaper). Reaper receives the MIDI data from Soft Arranger then it sends it to each instance of TX16Wx depending on the MIDI channel. Finally Reaper mixes the output of all the samplers adds some reverb and sends the final mix to your speakers or headphones.

If you prefer a different setup you can do it. The philosophy behind Soft Arranger is to be as open and flexible as possible. Maybe you prefer a different DAW, a different synth or sampler, maybe you want to use a multitimbral hardware synth or you want to plug it in to your hardware arranger. It’s up to you.