7-Zip is an open-source and very popular archive reader. CDisplayEx is a comic reader listed in SourceForge, with active releases but without any source files uploaded SF. It can support a variety of archives using 7-Zip plugins. I would like to suggest that the open-source 7-Zip project be taken advantage of in the development of Comix.
I'm currently using Windows and moving to Ubuntu soon, and it'd be fantastic to have a comic reader that can support the variety of archives out htere.