Firebox Help!

Hello i just bought a Presonus firebox and i love it. But i have 1 question?

I have a pair of logitech z4 speakers going in to my computer and i can only hear from one speaker at a time

When i plug my cord into the Guitar/Mic 1 i get from the right and when i plug into the Guitar/Mic 2 I get form the Left . WTF

Can someone help me i asked a guy at guitar center but said i need to change it from a mono? im new to this so could someone show me or tell me

I can iChat if someone is willing to help that would help a lot

Ps. im using Logic Express and Garageband

Thank you.