Dimension Pro is not a Multi-timbral synth.
That means you can only use it one track and one sound at a time.
However, you can load another instance of Dimension in another track.
For every sound you want, create another track and load-in another instance of Dimension Pro. You can select any sound for these other instances and you can create as many tracks as you want (as long as your computer can handle it, of course...)