Some icons aren't good with the ambiance or radiance themes because some symlinks are missing (for sound applet and notifications). I use this lines to correct the ubuntu-mono-light and ubuntu-mono dark icons theme (change the theme and apply it again to show the differences) :
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/audio-output-none-panel.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-output-none.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-high-panel.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-high.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-low-panel.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-low.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-low-zero-panel.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-low-zero.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-medium-panel.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-medium.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-muted-panel.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-muted.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-muted-blocking-panel.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-volume-muted-blocking.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-high.svg /usr/share/icons/ubuntu-mono-dark/status/16/audio-volume-high.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-low.svg /usr/share/icons/ubuntu-mono-dark/status/16/audio-volume-low.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/audio-input-microphone-high-panel.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-input-microphone-high.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/audio-input-microphone-low-zero-panel.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-input-microphone-medium.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/xfce4-mixer-record.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-input-microphone-low.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/status/24/xfce4-mixer-no-record.svg /usr/share/icons/ubuntu-mono-dark/status/24/audio-input-microphone-muted.svg
sudo ln -s /usr/share/icons/ubuntu-mono-dark/actions/24/system-shutdown-panel.svg /usr/share/icons/ubuntu-mono-dark/actions/24/system-shutdown.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-high.svg /usr/share/icons/ubuntu-mono-dark/status/22/audio-volume-high.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-medium.svg /usr/share/icons/ubuntu-mono-dark/status/22/audio-volume-medium.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-low.svg /usr/share/icons/ubuntu-mono-dark/status/22/audio-volume-low.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-muted.svg /usr/share/icons/ubuntu-mono-dark/status/22/audio-volume-muted.svg
sudo ln -s /usr/share/icons/gnome/scalable/status/display-brightness-symbolic.svg /usr/share/icons/ubuntu-mono-dark/status/24/mate-brightness-applet.png
sudo ln -s /usr/share/icons/gnome/scalable/status/display-brightness-symbolic.svg /usr/share/icons/ubuntu-mono-dark/status/24/gpm-brightness-lcd.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/audio-output-none-panel.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-output-none.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-high-panel.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-high.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-low-panel.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-low.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-low-zero-panel.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-low-zero.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-medium-panel.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-medium.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-muted-panel.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-muted.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-muted-blocking-panel.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-volume-muted-blocking.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-high.svg /usr/share/icons/ubuntu-mono-light/status/16/audio-volume-high.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-low.svg /usr/share/icons/ubuntu-mono-light/status/16/audio-volume-low.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/audio-input-microphone-high-panel.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-input-microphone-high.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/audio-input-microphone-low-zero-panel.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-input-microphone-medium.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/xfce4-mixer-record.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-input-microphone-low.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/status/24/xfce4-mixer-no-record.svg /usr/share/icons/ubuntu-mono-light/status/24/audio-input-microphone-muted.svg
sudo ln -s /usr/share/icons/ubuntu-mono-light/actions/24/system-shutdown-panel.svg /usr/share/icons/ubuntu-mono-light/actions/24/system-shutdown.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-high.svg /usr/share/icons/ubuntu-mono-light/status/22/audio-volume-high.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-medium.svg /usr/share/icons/ubuntu-mono-light/status/22/audio-volume-medium.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-low.svg /usr/share/icons/ubuntu-mono-light/status/22/audio-volume-low.svg
sudo ln -s /usr/share/icons/Humanity/status/22/audio-volume-muted.svg /usr/share/icons/ubuntu-mono-light/status/22/audio-volume-muted.svg
sudo ln -s /usr/share/icons/gnome/scalable/status/display-brightness-symbolic.svg /usr/share/icons/ubuntu-mono-light/status/24/mate-brightness-applet.png
sudo ln -s /usr/share/icons/gnome/scalable/status/display-brightness-symbolic.svg /usr/share/icons/ubuntu-mono-light/status/24/gpm-brightness-lcd.svg
sudo rm /usr/share/icons/ubuntu-mono-dark/icon-theme.cache
sudo gtk-update-icon-cache /usr/share/icons/ubuntu-mono-dark
sudo rm /usr/share/icons/ubuntu-mono-light/icon-theme.cache
sudo gtk-update-icon-cache /usr/share/icons/ubuntu-mono-light
Thanks, I'll review your suggestionand see what can be merged into the ubuntu-themes.