Have you tried Peak Limiter / Expander on https://forum.audacityteam.org/t/peak-limiter-expander/17790/3 ? See here for how to install Nyquist plug-ins http://wiki.audacityteam.org/wiki/Download_Nyquist_Plug-ins#install .
Have you tried Floorfish from http://www.digitalfishphones.com/main.php?item=2&subItem=5 ? See here for how to install VST plug-ins http://manual.audacityteam.org/o/man/faq_installation_and_plug_ins.html#vst_install .
I have good success using the shipped Clip Fix in Audacity to add a little more dynamics and “openness” in classical music (as long as the audio is not clipped or only slightly so). See http://manual.audacityteam.org/o/man/clip_fix.html . It can also be used after an expander.
I think Goldwave’s expander is quite good too.
Gale