Question about Logitech Z200

It would probably be easier and more sensible if you simply bought a 2.1 system (i.e. subwoofer plus two matching speakers).
Separate PC subwoofers are not offered and if you want to "trick" it together with a HiFi subwoofer, you need a suitable combo, the right intermediate cables, possibly even an amplifier... in the end too complicated & expensive, don't make your life unnecessarily difficult ;)