For dual filters I really like Rossum Morpheus Z Plane Filter and IME/Harvestman Bionic Lester as there are tons of sound shaping options and ability to even create presets for fast recall later.
I have Quadrax and the expander. Loads of fun and super powerful. Takes some time to learn but a great modulation tool.
Perhaps consider support utilities like a sequential switch and matrix mixer at some point. I use these utiltiies more in complex patches now. They cost less than shiny voice modules as well.