That is normal when u listen to CD or mp3.
However, there is a way u can hear 5.1 when u play CD or MP3, that is Dolby Digital's Pro Logic II.
Please read the following article firsthttp://www.dolby.com/ht/co.br.0107.PLIIListenersGuide.html
so, what is the best and cheapest way to enjoy Pro Logic II?
u can get the PowerDVD-XP (version 4), it had Pro Logic II decode function, so when u use it to play mp3 or cd ALL the speakers (5.1) will on