the pb/cb/yb holes are for an improved picture from your DVD player. check the DVD instruction manual. if it says that the player is a "Progressive Scan", it means you can use three cables to send the picture to the TV instead of just one. this gives you a much clearer picture, even with a DVD player. if you have a Progressive Scan DVD player, there will be three matching holes on the DVD player. The pb/cb/yb connections are strictly for picture... They do not do anything for your sound.
you might tell us what surround system you have, and then we can help more with your set-up.