Laptop Speaker setup help

[7ender]

Hello,
I'm working on a setup for my laptop but i'm not too sure how I need to wire it. I have audioengine a2's (self powered) and am getting a sub as well.

So I have a few questions. I'm planning on getting a behringer uca202 (http://www.amazon.com/Behringer-UCA2...547409&sr=8-1). I will then connect it's output's to my sub's inputs using standard RCA cables. What exactly does the uca202 do? I only found i'll need it through searching the forums. I was assuming it gave a line-level output signal, but if the volume is still adjustable through my computer, how is it line level? Would it be much better quality than plugging in through my headphone jack on my computer?

From the sub, i'll connect it's output's to my audioengines via another rca cable.

Would this be the correct way to hook everything up? Sorry I made it a bit confusing

Thanks