If you got a receiver that had 5.1 pre-outs, that could be a way to hook up to those speakers.
A DDTS-100 would also accomplish the same task.
That said, I think you might be best served by just changing your speakers to z-5500s or z-680s if you can find them. You'll get digital inputs in addition to a more robust system overall.
Low budget receivers tend not to have pre-outs, and the DDTS-100 can be hard to find now. I haven't looked what kind of cost there is to getting one lately.
For my suggestion of the z-5500s you're not only getting that same functionality, but you're getting better quality as well. If you can sell your z-5300s (or make them into a Christmas present for somebody etc.), it might not cost you much more than the Creative solution.
If you see yourself (despite not being "that big of an audiophile") getting some real speakers in the future, then the receiver route may be the way to go as you'd be leaving yourself a good upgrade path.