The SDS9 had two notable features. One was a chip that let you swap out snare samples (all the other sounds are synths). The other was a snare pad that had an extra sensor for a cross-stick/rim shot. I think the snare input, thus, may take a balanced 1/4" connector, unlike the other jacks which take standard "mono" 1/4".
Oberheim made a gadget called the Prommer that let you take samples and burn them onto an eprom. Also, the stickers on the back of the chips are actually functional - removing the stickers and exposing the chip to light will cause the contents of the chip to be erased.
While the pads are the visual appeal of the thing, you don't need to use them. First, you can trigger the inputs with audio, which gives you the option of having it generate new drum sounds off the input, or you can use it to generate midi events off of audio input. So it may be useful?
Also, you can obviously use something else as a MIDI master with it and finally, if you don't have pads/don't want to use them, you can build inexpensive triggers by soldering a piezo transducer from Radio Shack (Or your local equivalent) to a 1/4" jack. It's not the best trigger, but it works.
Many years ago, I think in Musician Magazine, I read a great description of the Simmons tom-tom sound: a sheep exploding in the distance.