CD burning is done within the audio software of the user's choosing. Since the BR-800 doesn't have a CD drive, we don't have specific instructions regarding the steps for burning a CD--as the steps vary heavily depending on the CD burning software being used as well as the CD burning software's version.
In most cases, audio will need to be mastered (mixed down) to two tracks in the BR-800; this mastered track is then transferred to a computer as a WAV file. The following article guides through this:
http://www.bossus.com/support/knowledge_base/208723666
After the mastered (mixed down) song is transferred to a computer as a WAV file, this WAV file can be used to burn an audio CD using CD burning software (such as Windows Media Player, iTunes, etc).
Please contact the CD burning manufacturer regarding the proper steps for burning an audio CD within their software.