You are thinking a mono synth just as well, I can see.
Why not a 16-voice poly or so complementing a 6-voice?
Something with almost endless headroom to find new territory is Prophet REV2.
- a 3rd aux envelope independent of filter and amp
- 4 lfo's
- true dual timbre if you want, or layer or split into two 8 voice synths with it's own effects too
- available as desktop or keyboard version
Nice with a two hand spread of 4 fingers each and create immersive soundscapes.