Well, this all depends how handy you are.
At first glance, the system unit sends all audio information to the subwoofer via a (1)custom cable, then the subwoofer does the amplification and sends amplified signal to passive (2)Front+Rear+Center speakers.
(2) is Easy, every speakers have + and - like any other Joe-Blow speaker. Hookup to any Joe-Blow amplifier/receiver.
(1) This takes a little investigating, must find out which wires of that custom connector carry what channel. Any electronics geek should be able to figure this out by process of elimination. U can keep using the subwoofer amplification (new box must have pre-outs), or let your new amplifier/receiver power the Front+Rear+Center (a more standard box without pre-outs will work here).