I've found the best way to set up the Prometheus for Mutron style sounds is:
LP
Envelope Up
Intensity on full
Then, as you know, the Prometheus can be set up like a static filter. Turn the Depth all the way down, then use the frequency knob to select the frequency you want. I use this to set up how much sweep I want. Turn the Freq. knob until you are pleased with where you would like the cut off point to be, then you can turn the Depth up until the envelope suits your playing style. I personally have Freq. about 11 oclock, and Depth at around 10ish. Then just back off the Intensity knob (or not, depends what you're going for!) until you're happy with the ratio of filter:clean.
Hope that helps!
Cheers