The themes need an instance of wordpress to work and so one workaround for your setup is to install each on subdomains and just make the main domain a landing page with links that leads to each install.
Please take note that the themes do not have an option yet for common login and so users visiting each site will need to register for each. Common login across theme install is possible through code customization. The AppThemes themes are not encrypted and so they can be modified according to your requirements. Implementation just depends on your coding skills or you can just hire a coder to do it for you. Appthemes also have certified community partners
http://www.appthemes.com/partners/ that can be contacted for customization job.
