"The ARP Omni-2 is an improved version of the popular Omni. It features all-electronic switching, single/multiple triggering and a separate bass synthesizer. The Omni-2 is actually three separate instruments in one package - 1) a highly evolved string chorus, 2) polyphonic synthesizer section and 3) separate bass synthesizer. All three sections can be played simultaneously for impressively-rich orchestral effects....The Omni-2 has controls to balance the volume of each section, selectable waveforms and chorus phaser controls. Each section has its own output so that the Omni-2 can be played in stereo or even dramatic 'triphonic.'"----[from ARP's promotional Omni-2 brochure courtesy of Kevin Lightner]
The Omni keyboards are string synthesizers with four separate voices (bass, cello, viola, violin, each independently switchable) and a bass/synthesizer section. The string section has its own variable speed LFO, and attack/release envelopes. The synthesizer section has a VCF and its own ADSR envelope. The bass/synthesizer split is set to the lower one and a half octaves.
The Omni (model 2300) was ARP's best selling intstrument. Unlike the original, the Omni-2 has single triggering so that when any note is held down the VCF and VCA envelopes will not re-trigger. The original Omni had multiple triggering so that every time a key was depressed the envelopes were triggered.
Adrian Cook of the Electrotunes,
Rick Greenwood of Foreigner,
Rick Davies of Supertramp - owned two,
Earth Wind and Fire,
Joy Division - Closer,
Manfred Mann's Earth Band,
Mushroom of Massive Attack,
Bob Seger and the Silver Bullet Band,
Allan Zavod who played with John-Luc Ponty
[Let us know if you have any further additions to this list.]