Help CV Output filter envelope for analog Filter

[malteEntzmin]

I have a broken behringer model d pcb and I managed to get the filter working. The Tsynth sounds amazing with the analog Moog filter. Now I would love to use the Tsynth's envelope to send cv to the filter. Where do I start? Which parameter do I need to convert to CV? I bought a MCP4725 and an opamp and I hope I can use these (Model D needs 0-10V). Would it be possible to have switch for the filters? Like a push button...A is the internal filter with the envelope (CV Cutoff fully open). B is CV cutoff with Tsynth envelope and internal cutoff fully open. And A/B is both filters controlled by the envelope. How could I overwrite the incoming frequency from the envelope and still use it for CV?
I hope someone can push me in the right direction. I read and learn stuff and I am okay with normal Arduino programming and stuff, but the Tsynth code is quite overwhelming if I don't know exactly what to search for.