Dear Dave_rosenblum: I think that a pair of Velodyne's in true stereo fashion will be a huge improvement on your system quality performance.
You have to think that when you " integrate " subwoofers in true stereo way the most important subject is that in that way you will lower the IMD and THD on your main speakers where now you can find that that main speakers are a lot better that what you are hearing today, you can't believe the huge improvement on the quality performance of those main speakers: just gorgeus!!
Other very important advantages on the subject are that now you will have not only a deepest low bass but with the right quality performance and the amplifier that runs the main speakers will perform better ( quality ) too.
As you can see the " reinforcement " of low bass ( if you take the right road ) could transform for the better the whole/overall quality performance of your home audio system.
Regards and enjoy the music,
Raul.