I would recommend that you take a listen to the newest iteration of the MartinLogan Dynamo subs. I am using a pair of the Dynamo 1100X's with my Magneplanar 3.7i's and they integrate very well. They have the advantage of Anthem Room Correction built in. As well, all of the settings can be changed from the listening position with an app that will run on an iOS or Android device. In my system the Dynamos replaced a pair of REL T-9's.
LarryRS
LarryRS