fail, welcome to the forums.
Looking at the manual for your sub it looks like you should have the front and rear connected to it, and using the two RCA input jacks for connecting to the computer, page 8 from the PDF found here,
Velodyne
Another thing is that your bookshelf speakers already have subs built into them (5.25"), which to me says if you want it to even come close to sounding right when using the sub you're going to have to play around with the bass redirection and cross-over settings.