Chad,
I have Vandersteen Quatro's and a single JLf113 sub. For 2 channel music I use the the Quatro's without the JL. I do not feel that they need any additional base support in either extension or volume.
I use the JL for home theater. I bypass the rears at 80HZ, run the fronts full and send the LFE to the single JL. In my room, 16x24X9, 1 JL is sufficient.
Hope this helps