Low volume levels on CDs that were burned on your computer from a BR-800 mix are usually due to lower mixdown levels when Mastering. In the BR-800, look at the “L R” level while Mastering and be sure that the meter is averaging as close to 0dB as possible--without going over and distorting.
If the meter is averaging around -24, remaster the song(s) with the “L R” meter level higher. This can be accomplished by raising the individual track faders and/or raising the MASTER fader when Mastering. This will allow the hottest volume levels possible to be burned to CDs.