It shouldn't be a problem but we would need more info on the current setup you have right now. For example if all the speakers are active(means they built in amps) you should be fine. It would just mean running the wires to the correct inputs.
Are they computer type speakers or home stereo speakers? If the new and old speakers are computer speakers it's just the matter of hooking them up correctly. If if are combining both home stereo and computer speakers it gets a little more complicated.