To get a system wide sound equalizer in Debian:
http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu/pool/main/p/pulseaudio-equalizer/
For my system I get this one:
pulseaudio-equalizer_2.7.0.2-3~webupd8~trusty1_all.deb
It will need this package:
# apt-get install ladspa-sdk
Then just manually install the .deb
# dpkg -i pulseaudio-equalizer_2.7.0.2-3~webupd8~trusty1_all.deb
In my menu I can now find: PulseAudio Equalizer