Fathom subwoofers?

I would recommend a better REL. if these two subs are in the same system… then it would be preferable to have two identical subs… definitely REL.

For audio systems subwoofers should always be used in pairs… assuming you can afford it. They really extend the soundstage. While bass is mostly non directional… when running left and right… it does a lot to better define the bass instruments.

What do you feel is missing with your current low frequency setup?

How did you determine your subwoofer's positions?

1) Deeper, more visceral bass. 

2) At present, I'm confined by "domestic considerations" as to sub placement and size, as my system is located in a Living Room rather than a dedicated listening room. (The room is approximately 14 x 24, with two doorways, woone double-wide, and a staircase to the second floor.) The REL is located in a corner, along the same wall as a pair of Sonus Faber Maxima Amator. I was thinking that a higher-powered sub of similar size might make an impact. That and the Fathoms have built-in room correction software. 

My experience has been adding a pair of S510s then changing to a pair of fathom113v2s and CR1. There has been an embarrassing amount of measurements and adjustments in this process as well as help with an acoustician. 

There is a size difference between them, but no question the fathoms are more dynamic and extend lower. LF extension can be a bit of curse because those modes become more difficult to manage. The LF trim on the fathoms works, but it is not that powerful. The output and dynamics are great, though. The features of the fathoms better enable room integration in terms of frequency response and decay but not impulse. They proved necessary in my case.

Their auto room correction will partially help with suboptimal room placement. It is not an entire substitute; nothing is. 

Despite your domestic considerations you should know the rooms standing wave bass mode locations by conducting the subwoofer crawl using your SB3000. The loudest modes are where your subwoofers should be or fairly close to. Using DSP to remedy a room null subwoofer placement is a stretch at best. 

Assuming your beautiful Amator's are -3dB at their rated 35Hz your T/9i will have already begun its roll off to meet its manufacturers rating of -6dB @ 27Hz. Richard E. Lord termed his REL's sub-bass speakers. Little has changed since. 

Both the F113 and the SVS are manufacture rated -3dB @ 18Hz. This lower response can embellish exactly what your seeking. I'm guessing despite their similar specs their overall presentation will differ but can be used together.

I had a JL Audio F113 A.R.O. (v1) for a short time. When I used the early Velodyne DD's twenty minute Auto EQ to Optimize that early F113, it responded startlingly well and gave up little if anything to the big 18" Velodyne. Point being while JL Audio's automatic only frequency leveling DSP works very well it's somewhat limiting. The CR-1 creates an all important detailed crossover region at a price. 

A few of the more important Optimization parameters Velodyne used in their DD and DD Plus series SVS has included in their current application. I would suggest seeing if the SVS can master control the Fathom. Hoping your domestic and technical goals can come together.

@richardmathes 

At this moment in time the best subwoofers are “balanced force” designs. These are being made by KEF, Martin Logan and Magic. 

The moving mass of a subwoofer is pretty high. Moving it rapidly 15 mm required a lot of force. Look at the magnets on sub drivers, BIG! When the cone is forced forward the enclosure is forced backwards. Put on a 30 Hz test tone and turn the volume up. Put your hand on the sub and you will feel it shaking. That is distortion. New designs place a driver at opposite ends of the enclosure operating in phase. The forces cancel out and the sub does not shake. 
 

If you want a more visceral performance from your subwoofer system you have two choices. You either increase the size of the drivers or the number of drivers. This assumes the use of good, powerful amps. I use eight 12” drivers in a room 16 X 45 feet.