Hi, I have one of these units and, as far as I can tell, if you can hear your music in the headphones it should be outputting from the line outs. If you cannot hear anything I would first check that the connection to your amplifier is good (RCA phono cables), that the correct line-ins have been used on your amplifier and have been selected (if you have multiple line ins, for instance on a stereo hi-fi amp), and that the amp is working with other devices (CD player, tape machine etc.) If it's working with your CD player, use that cable and line inputs with your BR-800.
If you can't hear sound on your headphones, check that the track buttons are set to play, the track faders are up and the master fader is up.
If you then still have no sound then there must be a fault with the line outputs. Hope this has been of help.