The Xpander is also a synthesizer module built by Oberheim. It is actually is two Oberheim Matrix 12 synths mashed together and is still thoroughly sought after by many musicians. The analog sound is extremely warm and real and the Matrix Modulation is so incredibly flexible that it can create a ton of varied patches that can be modulated in extremely interesting ways.
It also has a very unique chord rotation mechanism that allows you to trigger chords based on a single CV or MIDI note event and subsequent hits on that same note will create different chords, as they are defined in the Xpander's zones.
Michael Brecker used this synth (as programmed by Judd Miller to its fullest potential on tracks such as Original Rays.