Modular level is much higher than line level, so an output module (Ladik, Erica, 4ms, etc) will solve some of the problem. I believe, but I could be wrong, that the Doepfer mixer you're using sends everything out as mono signals. While I'm a big fan of mono mixes, the muddiness you are experiencing is likely due to the fact the the individual outs from your modules aren't going into a traditional mixer, then adjusted for the combined mono out.

It also occurs to me, that if each sound is being output first through its own VCA, you might have better luck with the output from the Doepfer (and its attenuators).