I had recently installed newest version of the songbird, but found out that equalizer preset could not be added to it because newer version of the add-on was not available. The workaround is mentioned below.
- Just download the equalizer preset + plug-in from songbird site.
- Open it with 7zip or other archive software.
- Open the install.rdf present in the archive and in the songbird section edit the em:maxversion to 2.1.0.
- Install the add-on manually by clicking the install and selecting the add-on from the file system and restart songbird.