Dear Peterayer: It's normal that the manufacturer advise be that you go for a bigger speaker in his catalogue.
Still today IMHO when we are talking of home stereo system subwoofers perhaps no one knows more than Velodyne. JL are good but not good enough.
In the other side, for integrate a pair of subs in a system the first issue is to know exactly what we are looking for and from my point of view the main targets are not bass impact or extension. We have to have very clear which kind of installation we will do where crossover frequency on the subs and main speakers is critical and it's from here where we can start to " build " the subs integration followed by the room subs position.
Yes, it is not an easy task but if you or the person that help you have the knowledge level then there is no doubt that you can achieve success about.
++++ " seamless integration " ++++, again with the right knowledge level that is IMHO always attainabel.
I took almost a year with my system to achieve that: " seamless integration " .
First decision you have to take on subs is to choose the right subwoofer and IMHO JL was a " wrong " alternative. It's not my opinion but there are facts about, example: for the model 212 JL gives an spec of 6.5% value for its THD at 50hz, this means that at lower frequencies as 20 hz that number can goes over 10% easily.
The Velodyne THD at 20 hz is only 0.5% and there are several reasons for that and one is the Velodyne system acelerator/servo that sense/measure over 15 K times each second the woofer movements to impede not only overload but to mantain inside that 0.5% THD. No not all subs are the same, but the important issue is the knowledge level we have.
If you are trying to add subs with high distortions you can't have success.
Believe or not IMHO the integration of active subwoofers in system with passive speakers is a " new science ".
Regards and enjoy the music,
R.