Comparison of various subwoofers for 2 channel audio

@drbond Your speakers are 7 feet tall. How high is the ceiling? If it is over 7' 2" tall the behavior of your speakers drop to point source at about 130 Hz. If you are crossing below 130 Hz it is probably more accurate to stick with the two subs you have, cross at 100 Hz and turn up the volume on the subs. They should be about + 10 dB. What are you using for a crossover? 

I have succeeded in bi amping the Sound Labs. Roger helped with the conversion. There are no passive crossover parts in the system. It was not easy going, but the end result is pretty amazing. 

I would drop SVS from your list unless you desire one note boom bass

Instead add Rel to your list. As well as KEF, Golden Ear, B&W.

I would drop SVS from your list unless you desire one note boom bass

That’s a misleading and inaccurate statement.  I have an SB2000 sub, and while certainly not SOTA it is absolutely not “one note boom bass.”  Further, there’s a member here who had both the highly-regarded Rhythmik F12 and SVS SB3000 in his 2-channel system and found them to be very close in performance to the point of being almost indifferent between the two, which certainly would not be the case if the SVS sub was that bad.  Personally I’d take Rhythmik over SVS albeit at a higher price, but categorizing SVS subs as “one note boom bass” is an over-the-top and ridiculous statement.  

Of the ones you mentioned, I'd recommend Rythmik.  Adding another pair of decent quality subs will help even out nulls and peaks in your room and give you more headroom (the ability to reproduce those low notes with little strain on the sub) when there is deep bass present in the music.  More subs can also increase the sense of "realism", that you're listening to live music, versus a recording.

The comment that SVS subs are only capable of "one note boom bass" is inane, or at best, uninformed.  I have a SVS SB12-NSD sub in my computer room, where I'm currently listening.  It's a small room and it's paired with small monitor speakers (Harbeth P3ESR) and quite capable of filling in the lower register that the Harbeths simply can't produce. 

There is no "boominess" or "one-note" character because it's the right sub for the size of the room and the speakers and is properly integrated.  It's very easy to distinguish the tone of bass notes.  The combination of the small monitors and the single sub provide a very satisfying experience and the feel of much larger speakers without overwhelming the room.

In general, internet direct subwoofer manufacturers are going to provide the best value.  The brands that dealers carry have huge markups for advertising and dealer margin.

My main system, which is in a much larger room includes two Rythmik F25 subs (dual 15" with 800 watts each) and two SVS SB13 Ultra subs (single 13.5" with 1000 watts each). 

The levels on all four subs are barely on, and for the majority of the music I listen to, you wouldn't know they are there, but they come alive when there is a lot of bass content in the music.  Not only that, but they create an immersive listening experience that is more like what you would experience listening to live music.  My main speakers are KEF Reference 1, which have surprisingly good bass for their size, but can't possibly reproduce bass that would be in scale with the music in that size of a room.

Again, right size and amount of sub for the room (possibly overkill), and integrated so that they blend well and complement the main speakers.

Rythmik F12G owner here.  I don't own electrostatics, but have Magnepan MMGs.  The F12G is very fast and musical sub that has a very good array of controls to match your listening preferences, whatever they may be.  Can't go wrong with a Rythmik, IMO.  It marries very well with my Maggies.  I cross at 80 after much experimentation with 60 (right around where the MMGs drop off) and 90.  A 90 Hz crossover made the Maggies sound too thin, 60 was a bit too congested-sounding.  80 was the sweet spot that really crystallized the Maggies and tightened up the bass presentation.