So what you are saying is that the 2nd router(DIR-600) is connected to the Linksys via a regular cable and you want to set up the hotspot on this DIR600? This would require a normal configuration on the ruoter, however you should turn off broadcasting of the SSId on the Linksys so that nobody can bypass the hotspot. For this reason it is normally recommended to install the hotspot on the router nearest your internet link.

See the setup guide: http://hotspotsystem.com/en/hotspot/install_guide_dd-wrt.html