In addition to Instrument Tracks we can also add an unlimited number of Audio Tracks in Studio One FREE.  Let's add some percussion to the second half of the arrangement by dragging audio loops from the Browser to the arrange window.

When using REX files it's even possible to drag single slices directly from the Browser. You can see all the contained slices below the file name and listen to them using the Browser's preview player. Quite cool actually!  By the way, the paid versions also offer the ability to open a new instance of Studio One's SampleOne by right-clicking on a REX file. All its slices are then already spread over the keyboard ready to be played via a MIDI controller.

Since there's only one stereo output, all the Audio Tracks we add have to be summed (and panned) in Studio One FREE and routed to SCOPE. In this setup I'm using Scope's ADAT input 9 and 10 for the audio from Studio One to Scope.