Need advice on subwoofer for maggies


I’m looking for suggestions for a sub to pair with my .7 Maggie’s. I had to sell my Magnepan 2.7’s along with my Vandersteen 2q due to downsizing. Yes - I am heartbroken 😢
I purchased a pair of .7’s and need a strong sub. Amp is a Adcom 5500 - along with matching pre. They sound great but I prefer a bit more low end. Any suggestions are greatly appreciated. 
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I must say I’m VERY impressed so far with these suggestions. I did purchase a SVS SB4000. I must say it exceeded my expectations. Incredible response and solid sound. So far I’m loving it. I’m still working with room placement and tweaking via app (super handy) but I think it’s a keeper. Thanks for the suggestion. 
I tried the Maggie’s bass panel and was not impressed. It was an improvement but weak and thin sounding. Thank for the suggestion though.
Interesting. I also have a pair of .7's.

My system is set up in my son's old bedroom and so it's in a smaller space. I'm using a pair JL Audio Dominion d 108's and to me, they're a perfect match for the .7 Maggies. 

http://www.jlaudio.com/d108-ash-home-audio-dominion-powered-subwoofers-96281