Seeking to Upgrade Subwoofer from SVS SB2000

My room size is 12 x 18.

I was considering SVS SB 4000 which is on sale for $1299.00 each.

I would buy 2, get a $200.00 discount for the second. I am very close to my $2000.00 budget.   

Thank you. 

This could be your luck day. I had 2 SVS subs tried all kinds of trick tweaks to integrate them. Go to VeraFi Audio >speakers as subwoofers>Vanguard Caldera 12" @ $399. Extremely well built and designed. Lots of great products at down to earth prices

@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.