Got this eml poly-box for some years now, i decided to put up some quick demo due the lack of info, and sometimes curiosity, about it. It´s is a cute, tiny, and exotic synth companion who basically turns a mono synth into a pseudo poly-synth (well not exactly, but more or less). I bealive it was designed to work with EML electrocomp series. So to take the best of it you need a modular or semimodular device i´d say. Here it is with my diy modular synth.
"From the Peter Forrest guide to all things synth: 'A curious and rare product - only 130 ever were made. Designed to turn monosynths into pseudo-polyphonics. Twenty-six "note memories." Connect a monosynth audio out to the PolyBox input, play a note on the monosynth, hold down a chord on the PolyBox, and the PolyBox will fill out the chord from the original root note. Then you could route the PolyBox back into your synth (if it had an audio input) to use the synth's filter and envelope. The PolyBox's own sound was limited to pulse wave
Here is how EML describes it: "Poly-Box is a pitch following variable chord generator controlled by your synthesizer and Poly-Box's own keyboard with built-in memory. Poly-Box takes a single pitch from your synthesizer and creates two banks of pitch sources. Each pitch bank contains 13 simultaneously available pitch sources at precise semitone intervals - covering an entire chromatic octave. The pitch banks may be in the same or different octaves, and can cover the range from one above to three octaves below the synthesizer oscillator."