Seeking to Upgrade Subwoofer from SVS SB2000

@deep_333 +1 The OP can buy two more SB-1000 subs and place them behind him as you suggest. This is the sub swarm concept. Spending $2K is a waste of money when the OP already has a capable pair of subs. A swarm of four or six subs will give smoother and more enveloping bass.

@deep_333 @jasonbourne71 +1  The swarm or distributed bass array of at least four subwoofers will essentially mitigate the rooms standing waves. No need for critical bass mode positioning while lessoning the load for each of the subs. 

Once I got my dissimilar subs gain balanced I found the room lock simply stunning.

Nice system selection by the way.

I recently added two F12 Rythmik subs to my system: Rogue RP-7 tube preamp, Odyssey monobloc power amps, Fyne -702 speakers.  The improvement was huge. total was just under $2500, close to your price for the two SVS 4000 subs.  And, they made here in he USA.

Hi, what I did recently I researched the top subs on the market and found my interest with the Rel. I contacted the Rel company and I sent Jacob the list of all my components and pictures and dimensions of my room from every angle. He got back to me promptly and suggested the best model from my specs and where to position the Rel S510 in the room. The service was excellent and quick. I bought the S510,was so impressed on how it upgraded my SQ that six days later I went out to buy a second one.With one, I was 80 % near the gates of heaven but with the second one I entered 100%.The coherence with everything together just took my system to another level. The Rels are a fantastic subwoofer company with lots of different models to suit one’s needs.

Your current subs should deliver plenty of bass.  Bass in a room is very dependent on sub placement.  In your room the most likely best placement is on the short 12' wall.  Place each sub up against the wall and 4' away from the front corners.  Give that a try.  Depending on where your main speakers are located in the room, you may have to play with Phase to deal with the time delay between the mains and subs.  Also make sure you don't have the two subs out of phase from one another, if they are they can be cancelling each other out.   Also don't cross your subs over too low.  My experience has been the crossover points typically need to be between 50 and 80 Hz.  Below 50 Hz, output can drop way off and above 80 Hz you can start audibly hearing where the subs are located, which is undesirable most times.