Is it usual for CD audio to only...

[GremlinHater]

play in the front two speakers of a four speaker setup? Cause that's how it is with mine, MP3 and stuff sounds in quad mode, but CD Audio only pumps out of the two front.

 

[Zepper]

CD audio is a two-channel analog signal. Your sound card would have to provide some sort of quad simulation for you to get rear channel output. Most cards do have some sort of quad sim, just need to find out how to enable it on your card. If your card came with its own media player, it will probably have a button to turn quad sim on and off.
.bh.