via this auction
"This synth is fully functional, and with regard to appearance - I would give it a 9.5 score out of 10.0. The previous owner took exceptional care of this instrument, and the only noticeable wear is a small, round paint chip on the back panel.
The Siel DK-600 was made in Italy in the mid 1980’s. It is a classic and even a “sleeper classic” in my opinion. A google search will turn up all of the details including the detailed description from vintagesynth dot com which states… ”The DK-600 is Siel's unique Italian take on the mid-eighties programmable polysynth with MIDI implementation (badged as the Opera-6 in the UK). Just like the Juno-106 and Poly-61 of the time, the Siel was a 6-voice synthesizer with straight forward programming, simple effects and digitally controlled analog oscillators (DCO's). However, the Siel, having dual oscillators per voice sounds thicker than the Juno or Matrix because it's got 12 oscillators! And because they're DCO's, you know they'll always remain stable and in-tune even though they are analog in nature. The DK600 has many other nice features such as complete MIDI implementation. There are 3 LFO's for extreme modulation. Both the filter and amplifier have standard ADSR envelope sections. And like similar synths, all the sliders and buttons are intuitively placed on the front panel for hands-on real-time programming."
