I just swapped my Roland MKS-70 for an SCI Six-Trak. I felt that I needed an American VCO poly in my collection. There aren’t many affordable ones available, but the Six-Trak is one. I also have a Roland JX-10 which is the keyboard version of the MKS-70.
Design wise, it’s kind of a strange combination of 80’s high tech and 70’s vintage. While it has the classic Sequential Circuits logo and solid wood sides, it has a “digital” user interface. You select a parameter number on a keypad and set the value with a pot. This is probably a big reason for why it’s not more expensive, kind of like same thing with the Roland JX:s. However, it’s actually very easy to work with, and there’s a nice template for Ctrlr available. The Six-Trak has a very good midi implementation – each parameter is can be controlled by midi CC (!) and not sysex which was the common and annoying way back then.
The cosmetic condition is very good on this one, I heard it was previously owned by the guy who managed SCI imports to Sweden back then.
Soundwise, it’s not a Prophet 5. Compared to the Roland Juno-6, which also is a one oscillator poly, the Six-Trak sounds very weak. To come alive, some external effects like chorus and reverb is recommended. There are no built in effects.
However, there’s a unison mode that definitely turns the Six-Trak to an monophonic monster! This mode can make it deliver extremely fat leads and basses.