Hi Guynemer,
These errors appear because the Hekkus library isn't linked. You can add a library by editing your project .epj file with a text editor. Add a new line at the bottom:
staticlib = "hss.lib"
Also, copy hss.lib from Hekkus into your Symbian SDK installation folder: /epoc32/release/armi/urel
If you don't want to copy this library you may also specify the location of the library directly. For example:
staticlib = "c:\projects\HekkusSoundSystem\lib\symbian-armi\hss.lib"