DSPeaker Anti-mode 8033 ii works wonders with my new sub

Good to hear you like the Antimode. When I acquired mine I called the manufacturer in Finland and talked with one of the engineers: with the Antimode the best position for the sub is well into a corner. This gives maximum corner reinforcement for more power, smallest dips, but also biggest peaks. The first two effects are an advantage and the peaks can be dealt with by the Antimode. It works well, and in many situations the sub will also be less visible.
I am similarly saving for a second sub. That will not be stereo, but dual mono. The Antimode 8033 does not have stereo outputs, and that would not be quite so desirable either. At these frequencies bass is completely non directional, and dual mono subs give a smoother response than stereo subs.

Dual mono is also preferable as it produces a smoother equalization. At such low frequencies sound is omnidirectional in any case.

So you don't need a second 8033 or a dual core. Since you can invert phase on the SB2000 you do not even have to get a Y cable.