You can use SoundStage to output to a line level input like a sound card or mixer without attenuation, just back off the Output Level control appropriately.
Regarding running line level sources through SoundStage, if you run line level in you get line level out, but obviously if you input a mixture of line and modular level sources in you’ll have to attenuate the modular level sources to have them at the same level as the line level sources.
