Connecting Bookshelve Speakers to PC

I want to connect a pair of Linn 5110 speakers to my PC. I think I need to get a sub and power the speakers off of the internal amp and run a mini DB cable for the line out of the PC to the sub. Is this correct? Can anyone recommend a sub to do this with? All of the subs I am finding have RCA out for H.T. Am I missing something?

Yes. An amplifier. Powered subs generally have a power amp only for themselves and you need to add a power amp for the bookshelf speakers.
I would like to find a powered sub for speakers. I mean all computer oriented speaker packages have an amp for speakers. Bose have a built in amp for speakers. I would like to use my current sub the speakers terminate into what looks like an old AT style keyboard plug. I think Bose just terminated into an RCA

If anyone is following this tread, I found a couple of subs to power speakers: Phase Technology's Velocity HV-800, 1000, or 1200 and the JBL E150P and E250P. These two have line in and front speaker hookups.