I'm certainly no expert in the field of audio but I do remember reading about a program within Linux that adjusts volume levels to a standard level. Is this what you were looking for? (Linux Format magazine ran a tutorial on running it sometime back - might need to be a subscriber to access the archive though)
Anyway, this program is in the repos and called 'normalize'. Don't bother looking for it in the menus after installing as its a command line program. And much easier to batch process many files because of that.A search for 'normalize' will also discover other plugins/aids which may also be useful to you.
More info at:-
http://normalize.nongnu.org/README.html(Obviously, you don't need to run 'make install' as you already have the latest version 0.7.7 in synaptic)
Hope this helps,
Regards,
Blarney