2.1 speaker systems such as the Dell A525 have ONE input to the speaker system from the PC (the green connector) and the bass speaker in the system houses the power amplifier and distributes audio to the smaller speakers.  That is a special cable and I doubt that you will ever find one.

I don't think you can hook up the way you want, but all you have to do is connect the original audio input cable to the speaker system (the cable with the GREEN plug) into the low frequency output on the PC and then change the speaker type to 4.1 or 5.1.  It MAY work and MAY not.    If that doesn't work, get a "Y" cable with one 3.5mm stereo plug and two 3.5mm stereo jacks - connect the Roland speakers to one jack and the bass to the other. 

I didn't know Roland made amplified PC speakers?  I'm a musician and use a lot of Roland stuff.

Not sure if this place (monoprice.com) has what your looking for or whether you've already tried them but they have had everything I have ever needed.

Thanks for the tip DCX. I appreciate it and I'll give it a try.

Fireberd, one more thing. How do you like the Sonar 8 for mixing? I had the 6 but my evaluation time ran out before I had a chance to use it. I want to start mixing her at home but I'm wondering between Sonar and Reaper. Wha'cha think? I've got chops for Nuendo but it's out of my price range at the present.

Thanks so much Fireberd. You have the best solution so far and I'll try them both. As far as the Roland speakers, they are called Stereo Micro Monitor MA-8. I've just laid them on their sides with the ports and tiny tweeters on the outsides and they fit perfectly on my desktop. I'm a 40 year veteran recording engineer and I'm embarrased that I can't hook up a simple sub woofer, but this has been a booger bear of a problem for me. Thanks a bunch for your suggestions. Incidentally, the Rolands have a mic input, bass and treble control, volume control, with head phone input on front, but they are a bit mid rangey, but they still sound pretty good compared to the Dell 2.1 toy speakers. However, I do like the powered subwoofer. In addition to be a long time recording engineer beginning in Muscle Shoals, AL during the 70s when we were cutting so many hits we were going 24/7 almost, I'm also a bass player myself. Google "Jerry Masters Engineer" and the click on Discography and you'll see just some of the records I've done over the years. I'm not trying to blow smoke but it's nice to get advice from a peer and someone who thinks the way I do. Thanks again. I'll let you know how it turns out eventually. http://www.prlog.org/10468749-rock-and-roll-icon-jerry-masters-new-book-hanging-from-tree-by-my-knees-set-to-release-1252010.html

Jerry I like Sonar 8.5.3. I have the Professional Edition, but I only have a small home studio.  But, I've done a lot of recordings for locals, a "country" session for Bluegrass singer and ex Bill Monroe guitar picker Bill Box and for ex Nashville songwriter Jimmy Peppers.  Jimmy says the sound is as good as the "Barn" although I doubt that.  Peppers was George Jones' band manager in the "no show" days.  Peppers was sending the last demo session I did for him to a contact he has in Muscle Shoals.

I can't compare Sonar to anything else as that's the only "professional" recording software I've used. 

My main instrument is Pedal Steel Guitar, although I also play bass and some lead.  In the early 70's I worked as the amp tech at Little Roy Wiggins "Music City" music store on lower broadway, across the street from Tootsies.  My web site is www.gulfcoaststeelguitar.com  and I also maintain the www.floridasteelguitarclub.com

Try my suggestion, with the Rolands, that sound like they are or could be studio monitors.  I've got a pair of Samson Resolve 65a studio monitors that I use.