Recommendation for sub with high level inputs

This is what I would recommend and suggest for you.

A pair of REL T7x. One for each side. It's the best way. 

rel.... 

Rythmik Audio offers high level and line level inputs on the non-XLR versions of their "standard size" plate amps  Models with 8", 12", 15", and 18" woofers---and multiples of same (including dual opposed)---are available. Competitively priced.

Tekton.  Just hooked up my lowest tier 2-10s (pair of em) and .. wow.

You can get 2/4/6- 10..  2x10 is equivalent to 14”, but smaller, lighter faster. With integrated 300w amp.

On high level ins for right now waiting on some cables.  

seriously have never heard metallica or Iron Maiden sound so good.. the  bass kicks just pop.

(they also have larger ones too, but I would use those for home theater)

Rel and Rhythmik are great suggestions.  Whatever you do I’d highly recommend getting a pair of subs.  On the cheaper end you could get a pair of SVS SB1000 (non Pro) subs from their Outlet for only $900.  They’re only about 13” square but will still get you down to an honest 20Hz (-3dB), and they offer a 45-day risk-free trial including shipping both ways so you can see if they work for you.  Hope this helps, and best of luck. 
https://www.svsound.com/products/sb-1000
 

Video: only single sub to add Jurassic Park Dinosaur Stomp.

Video and Music: two subs, hopefully located adjacent to the fl and fr.

Low Bass may start out room filling mono, no direction home, however the many overtones definitely have directional info, thus a Stereo pair of subs is desirable.

I'm no fan of ports, and of course self-powered sub(s) helps your main receiver/amp.

Depending  on budget , Svs SB- 4000 sealed subs are more accurate then any vented sub ,the sub weighs 102 lbs even 1 sub sounds excellent and very powerful and theSVS has a great app ,5 year warranty , free delivery 45 day trial , and even free return f not happy 

Rel T7x or T9x for sure. Both are very musical subs that will integrate with your speakers and amp very well.

HSU...Overlooked way too many times and priced much better than many.

https://www.hsuresearch.com/

++1 @scm Dont know why Hsu doesn’t get more love on here. I own two- for AV room and my home recording rig. I’m integrating from the preamp and AV prepro. Since Hsu is self powered, less strain on the mains. Seamless… 

+1 for REL X 2.

I own 2 T9x with a hybrid Yamaha 5.1 / Raven 2 channel system in a relatively large room and they kick. 

if one is trying save some $, the prior rel t-i series are very very good too (t7i, t9i), for less money than the x series used, which makes a difference if one is going for a pair of them... 95% of the performance in my estimation

Why not a Sonus Faber Gravis ii?  Same lineage as REL.  Buy one now and a second later.

https://hometheaterhifi.com/reviews/speaker/floor-standing/sonus-faber-sonetto-iii-speakers-with-gravis-ii-subwoofer-review/

Rel and Rythmik are great suggestions. Rel from personal experience, Rythmik just from what I've reviewed. Personally, I own dual SVS SB1000 Pros that are fantastic, get low as mentioned earlier, and biggest benefit is you can control them (filters, volume, etc.) from your listening position via an app.No going back and forth and crawling around.

+++1 @scm, @zgas-music, HSU you can get 2 of the VTF-2 MK5's for around $1,500.00 or better yet 2 of the VTF-3 MK5 HP's for around $2,100.00 they are easy to set up and have plenty of options for integrating them into your system.

This JL Audio d110 has high and low level options. I’ve owned one and I would highly recommend it.

https://www.jlaudio.com/products/d110-ash-home-audio-dominion-powered-subwoofers-96283

My REL S-812’s got a sonic upgrade when I attached DIY "grounding boxes" to their RCA plugs.