You can use a DR3 Remote to select one of several stereo inputs. Here’s a video showing how to set up Halogen to do this for two stereo input sources.
This Halogen tutorial video shows how to link pairs of stereo zones together. Specifically, it does the stereo linking of Selectors and Levels within the Zone Processor DSP block in Halogen. This allows one DR3 Remote to select one (of two) stereo zones. It also shows how to link the left and right output volume controls together for stereo volume control.
Here’s a second video tutorial, shows how to mix two stereo input sources in a single DR3 Remote.