Agreed ^^^^ on finding sweet spots being a challenge with the CS-15. I modified my CS-15 to make the channels switchable to serial, which makes it even tougher to dial in a good sound, but once you do, dayum it's righteous. Like a single Virus voice, only bigger and fuller.
The CS-15 filters will not self-oscillate without some external assistance. You have to create a feedback loop from one of the outputs back to the Audio In. If you use the Headphone out, you can get some nice distortion pre-filter, very grungy, much like the Korg MS20. There is still this annoyance in that you cannot change filter key tracking. It's stuck in one position, and that unfortunately is not 100% in line with scale. Otherwise I love the sound of it, especially bass with pulsewidth modulation. Instant Front 242, circa 1982.
"Lots of people are nostalgic for analogue. I suspect they're people who never had to work with it." - Brian Eno