The Sub Active has the same preamp as the Stingray 2 eq. THe SUB active has a very similar sound to the 2 band Stingray. It is not identical but for half the price it is very close. The SUB passive has no preamp ,no active electronics. It has a big thick warm retro sound. For passive lovers it has a rich tone, but less on that high end spank that you would normally expect from an active Stingray.
The Main difference is the Stingray is made from Ash. The SUB is Poplar. Two different woods can contibute to the overall sound. The Humbucking pickup is the same in all the basses.
If you're a fan of the Stingray, you definately shouldn't get the passive SUB. If you get a SUB, get the active one. It's only about $50 more than the passive version at most guitar shops. I myself considered buying a SUB a while back. I compared it to the Stingrays and Sterlings at 2 different guitar shops. The similarities in sound blew me away... until I picked up the passive one, haha. Long story short... get a Bongo, haha.