I use the Hsu Research VTF 15H MK2 subwoofer with my Poseidon speakers , it is fast , has variable tuning features goes down to as low as 16Hz ( no music their) it's not boomy but the vibrations are felt in your chest and your sitting position , for music I use it in a sealed mode and it sounds sweet blends so well that I don't even notice it is playing , and it is very reasonably priced .One draw back it is Huge ! with a 15" paper cone woofer weighs about a 110 lbs.
Has been reviewed in Audioholic online A/V magazine 2015
Home Theater Sack " the best of Axpona 2015"
David Vaughn , " Sound and Vision " Feb/Mar 2015
Brent Butterworth , "About.com" December 2014
last week I switched it over to my HT system with my newly acquired Wyred4Sound multiChannel Amp MC 7150 directly attached to the OPPO 205 UHD via 7.1 channel connections and played the movie "Gravity" the experience was mind blowing in the Home theater environment their was no boom but the home was shaking and the windows were rattling and the Couch I was sitting on my butt was vibrating ! Switching it to the music system in a sealed mode , it blends so well that you don't even know if it is there.