The S206 is based on a 4 pole cascaded sallen-key topology with a special feature where the pole pairs can be separated from each other with knob/CV control over the separation amount. This configuration is useful in creating a wide variety of vowel sounds that are otherwise only approachable through more advanced patching or through audio rate modulation of filter cutoff of a casual filter (and even that is limited).
Most of the controls are self explanatory. When separation knob/CV is at zero, the 4 poles are all at the cutoff frequency at which point the filter is a 24db/oct. Once sep goes higher, two of the poles will go higher than the cutoff and other two will go lower*. The shape and slopes are rather complex here and can’t be explained as mere 12db or 24db.
An added feature is a cas/par switch. Cas is the normal cascaded mode just described above. Par however, splits the cascade and runs the two sections in parallel where the output is a mix of the two sections. This gives a different flavor of the vowel sounds but without a steep 24db slope when sep is close to zero.
*Think of two poles as a cutoff peak.