No, this option is not available in BBC SO Discover or Core. The option for Multi-Outputs in the BBC Symphony Orchestra Plugin can only be used by the Professional element of this library, and pertains to the microphone outputs on Pro.
If you wish to achieve a surround sound with BBC SO Discover/ Core, you can of course split the stereo output into a 5.1 signal, or use multiple MIDI track instances to create a fake surround.