You could use ladspa-plugins to do so. There are
several EQs, that do what
 you need. There's Steve Harris' eq (ladspa ID 1199 I believe) and then there
 is Fons Adriaenson's parametric Filter, which you can download from his site.
 It's better suited to the task, I think. It only has 4 bands, but there are a
 lot of possibilities to configure the bands. Besides there is an EQ in the TAP
 plugins.
   You can find links to them all on
 
http://linux-sound.org
  or at
 
http://apps.linuxaudio.org
   To involve them into your alsa system (app-independent) there is an
 alsa-plugin, that supports ladspa-plugin integration. I don't know the exact
 syntax or the name of the plugin. But you could have a look at
 
http://www.alsa-project.org
   Look for asoundrc. It's a configuration you do in your .asoundrc in your
 home-directroy or in /etc/asoundrc (not 100% sure about the latter name, never
 did it).
   Hope that helps. If you've more alsa-specific questions. You could try on
 this list or directly mail to the alsa-user list. 
Thanks Julien,
I've got the TAP plugins installed and I'd like to involve them in
app-independent ALSA just like you describe.  Is there another ALSA
plugin I need to install to enable the TAP plugins or should I start
editing asoundrc?  I will ask on the ALSA list if no one is sure how
to proceed from here.
- Grant