at 1500 bucks I'd be looking into a studio electronics atc-1 or se-1 ( new series are atc-x and se-1x ). The atc-1 is the best sounding monophonic synth which is completly analogue, by default it comes with a moog filter but works on cartridges to add other vco's from the tb303, oberheim sem, arp2600 and the minimoog. The se-1(x) is a 6 voice polyphonic analogue, giving less power when patching for a bass ( but still yo, it whoops your mixer/audiocard's ass, my a&h is on the -30dB pad lol ). They both have what it takes to bring out a raw punchy sick bass but since the se-1 is poly it wont put its brilliance in the low range alone ( which goes for most poly's with a lot of voices, layering eats headroom in any case ), so if you want bass pur sang then go atc-1, you want leads n pads n bass then se-1 cuz it will rip any motif, triton or whatever to bits. They both should come below the 1K and for both cases I suggest getting a nice hardware comp to keep that bass signal chain under control because these beast make you inputs peak really fast, I'd definitly would look into a good deal on a focusrite compounder ( it has a very nice bass enhancer, I use them on kicks n bass of course, but you can give snares that nicey subtle bottom too just dont overuse it hehe).
On a note, I think the gear you have now are still appropiate for creating bass, its not the synths because in those terms ( of who has the best bass ) is a matter of knowing the vintage classic stuff. I personaly im addicted to the acces virus, those machines just really whoops anything and falls into a mix by itself.