Subwoofer Cable Connections and Selection

I'm a little confused about connecting my sub to my pre via line level.   Right now I have a 4 meter cheapo RCA interconnect that I probably got at Best Buy and want to upgrade. My pre has a L&R line out and my sub has a L&R line in.  But all the sub interconnects I see are sold as a single cable.  Everything I am reading online assumes there is a sub out on the pre and then that can go into either the left or right input on the sub.  But I have found nothing on a pre with left and right.  Can I just get a single interconnect and go from the pre left to the sub left and leave the right open on both?  Maybe the two outputs are to feed two subs?

Also, I see many sub interconnects w/ and attached spade connector.  I don't think I can use that.  How would that be used?

Here are a couple products I found that would be in my price range (<$200)

• http://www.analysis-plus.com/product/home-audio/interconnects/sub-oval-interconnects/
  
• Bottom of page:  http://www.audioquest.com/analog-interconnects/

I have a Cambridge Audio 851N and Velodyne 1215X.  

Thanks.

Ken