GTK+ for Linux

Don't you already have it? All major Linux distros (that I know of) come with it pre-installed. If if you really don't have it, the distros that have Gnaural natively (Ubuntu, Debian, SuSE, Gentoo, ArchLinux) would automatically install it as a dependency.

And if that didn't help, this (being the source of GTK+) will definitely solve your needs: http://www.gtk.org/


Gnaural/Gnaural2 for Linux:

If your distro doesn't already offer it natively (see above), or you can't install the Debian-style ".deb" package file (native to Ubuntu and Debian), don't fret: it isn't hard to compile the source code yourself. Just download the Source .gz file and follow this README. You can basically just run the executable (which gets created in the src/ subfolder) without any further "installation" -- but do note that Gnaural2 requires the included "gnaural2.glade" file (also in that subolder)to be where it can find it (since that is how it knows what sort of GUI you want).