I think the SB2000 would be perfect with the SB13. They both seem to go down to a similar frequency. I'm guessing the 13 is just that much more powerful all the way through?
It would add just that little extra punch, you might love it! See with mine one goes down to 19 and the other only to 26 so the NSD has to handle the real lows by itself. But I like it that way, it's cheap. And I get lows, plus punchy mid bass.
Main room (3D blu ray, PS4) - LG 65EG9600: Denon x4000, Klipsch RC-62II, RF-62II x2, RS-41II x2, SVS PC-12NSD + Klipsch RW12d
Couple small LCDs - PS2, PS1, Dreamcast, N64, 3DO, Saturn and other various retro game collections MINT COMPLETE games