Hi @brad,
thanx for the detailed answer - I did read it all 
So essentially I can proceed as intended - boosting signal levels to drive plugins as hot as I need, lower the level at the output stage of a rack to be sure I have enough headroom to mix everything together and then raise the output level at the end of the chain to maximize S/N ratio of my sound card.
One Q: can you say a bit more about the output limiter (found nothing in the Guides section)? if I select a threshold of 80%, does that mean that anything above 80% is flattened - or does it mean (my assumption) that the volume curve is linear up to 80% and then a gentle tanh(x) slope levels everything out up to 100%?
This would mean in musician’s term that the volume increment from 80% to 85% is still significant, whilst the increment from 95% to 100% (full scale) has a lot less impact (and any peak overshoot beyond 100% is simply flattened to 100%) - correct? So no harsh digital clipping should occur (within limits - driving a limiter too hard still sounds ugly 
) even with the level meters hitting full scale…
Cheers,
Torsten