Its not advisable to change speakers on those HTIB systems they are not very flexible like regular home theater gear and usually the speakers are made to go with that particular amp only...the main problem is the impedance usually the impedance on those speakers is odd like 3.5 ohms or 3.7 ohms, so you need to find out what impedance they are before changing them out if they were 3.5 you could probably get away with 3 ohm or 4 ohm speakers but not much else, also you usually will not get much better sound either as the amp in those systems is limited in output and quality so even with new speakers will sound about the same with limited output...
