I am playing Cd's and have a pair of Definitive Technology- Model BP-10 tower speakers connected to my Technics SA-DX1040 5.1 Channels Receiver and while the music is playing, all of a sudden the music seems to cut out and plays at a much lower volume and a tinny sound. What could be happening here?

Amigos tengo technics sa dx 750 necesito codigo para control remoto RM Y 181 gracias quien pueda ayudarme

There are 2 major possibilities and since you didn't say if the sound comes back here's the general split.
1. The power amp section could be having problems and/or protection circuits are kicking in. In this case repair of the amp will be needed.
2. There is a bad connection somewhere making the audio path go bad. In this case a good can of contact cleaner applied to all switches and controls may help. If not, the bad connection may be internal. If tapping (or rapping) on the unit makes it come back, there's probably a bad internal connection.
If letting the unit cool down brings back the sound, its the power amp section.