I came across two ridiculously good tutorial videos on mastering from FabFilter. Mastering engineer Dan Worrall demonstrates (in REAPER 4) how to use some of the FabFilter plugins for mastering.
The MS mode for the sidechain is droolworthy almost, I’m going to have to check these effects out myself.
Dan’s parallel upward compression trick is something I can definitely put into use right away. Even if you don’t use FabFilter plugins these videos are definitely worth watching.