PC/Desktop speakers with extra inputs do exist. My Altec Lansing speakers (old model, so no doubt discontinued) have two, for example.
Hi Laust! I think we talked about your speakers some months ago on another topic
I have searched eBay for similar speakers, but since it's not a common feature, it's hard to build a search about it ("twin inputs" ? "two input line ins" ? )
Any chance you could take a pic of the inputs of your speakers?