My upgrade sub budget for 2 subs are $1000.00 total. The Martin Logan is adjusted properly and I find the bass a bit weak. The current 2 subs help, but I would like to do better.
Budget is too weak for a sub upgrade. You can’t do any better than your current SB2000s with such a budget (i.e., there’s nothing wrong with your subs).
I would wager that it has everything to with incorrect sub placement and incorrect integration with your mains.....because those 2 subs should give you enough bass to hit the brown-note (better than miralax) if you cranked it all the way up.
Without knowing anything about your room dimensions and whether you have a measurement mic or not....try as follows.
If you have them on the front stage, move them on both side walls behind your listening position (not too far behind). It should cancel out some key modal nulls and give you a feeling of envelopment. You probably have the crossover setting very low because you saw the printed frequency response spec from the manufacturer perhaps. Turn the crossover up fairly high, 100 hz or so (you won’t localize a whole lot with the dual subs in such a position). Last but not the least, fine tune that phase knob. Last i recall, SVS gave you a continuously variable rotary phase knob, not a rudimentary 0/180 flip switch like Rel or something...