Subwoofer Suggestions

I suggest Rythmik. As good as REL and less expensive. Try here.

I tried 5 different subs (all under $400) and could only afford one vs 2. I lucked out, the one that worked out the best is a 10" Polk from shopgoodwill for $25. Everything else was a giant mess, sound-wise. I am looking to score another Polk. I am using the speaker connection, the experts told me that's the best (besides that my amp has no sub out).  

Unless you have an expensive setup, I wouldn't "outclass" it and outspend on sub(s) with REL or SVS.

I also tried managing the frequencies with splitting it between the sub and speakers but of course that costs money and I wasn't that lucky with my purchase in that area. 

You could also search the forum for previous discussions, there has been a wealth of knowledge and case specific advice here, all I know I learned from here. 

I have owned many subs in my lifetime, and at your price point, I recommend the RSL 10S MK II. I own the 12S, and it replaced a pair of high quality subs (I will not mention the name here, as I do not want to offend anyone or any brand). My best, MrD.

No love for SVS here? I'm also looking at the same choices and it looked promising. Is there an issue with them? 

Everyone has their favorite brand. SVS are fine subs.The equalizer has an app that you can install on your phone or tablet and do all the adjustments from your listening seat.I'm very happy with mine.