I know there are some who have problems with Soundflower, but I'm unclear what these are - I used it a lot without issues. Perhaps this would work for some other situations like those discussed here. When I did this on an older OS version I was able to include the document as a startup item, making the whole thing transparent. AU Lab provides inserts, sends, faders, balance etc, to control the sound, and has documents with the i/o and mixer settings saved.

AU Lab input is set to Soundflower, with output to the Mac outputs connected to monitors. I tried routing system output to the 2 channel version of Soundflower, and having AU Lab (from iZotope?) running. There are lots of proposed solutions in google, but most involves paid software to achieve very simple utility functions. All I wanted to do is apply plugins to the system audio output on a Mac used as a media centre. I had a similar requirement to get around recent British television production standards that require actors to mumble and background music to be 30 db louder than dialog.

How to eq microphone for skype calls