Welcome to the Support Communities!
The share to DVD settings in Final Cut Pro X use the Dolby Digital settings which are stereo for DVDs. So this can’t be done directly in Final Cut Pro X.
The link below will explain the Dolby Digital parameters and options in Compressor 4. You may need to research a different DVD authoring software to achieve your desired result.
Dolby Digital - Compressor 4 User Manual
Dolby DigitalThe built-in Dolby Digital settings (in the Create Blu-ray and Create DVD destinations, as well as the built-in AC-3 and EC-3 audio settings) use the Dolby Digital transcoding format. This format encodes Dolby Digital (AC-3) and Dolby Digital Plus (EC-3) audio files that contain multiple audio channels, including 5.1 surround sound. You can also create custom settings that use the Dolby Digital transcoding format.
Note: All files intended for video and audio DVD authoring must have a 48 kHz sample rate as required by the DVD specification.
- DVD Video: Choose this option if you’re encoding for use in a DVD video authoring application.
- DVD Audio: Choose this option if you’re encoding for use in a DVD audio authoring application.
Tip: For stereo encoding, rates of 192 kbps and 224 kbps are typical and will produce good results. For Dolby Digital 5.1 encoding, a rate of 384 kbps is recommended. For 5.1 Dolby Digital Plus encoding, a rate of 192 kbps is recommended.