First, try running
from the command line. If there is still some headroom on any of the sliders, bump them to 100%. Sometimes there are weird interactions between the different volume sliders, and making them all 100% could increase you output volume.
IT AIN'T ENOUGH
For even more volume, we can head to the commandline.
will list all possible sinks for volume increases on your system. To bump my volume to approximately 200% (100% is 65536), I used:
pacmd set-sink-volume alsa_output.pci-0000_00_1b.0.analog-stereo 125000
This will increase noise to some extent (looking into some good ways to filter it), but at least those quiet sounds can now be heard!