Router mode the Almond will act as a full router and only requires a modem connection, it will have control over the DHCP and all other router functions. Access Point mode it is just providing internet access to devices connected to it but that service is being routed through whatever router it is connected to. In your case if you set up the Almond as a router you would have a Double NAT because you'd have one network off another. Depending on what you want to do both can work but the simpler option is to set it up as a wired access point in that situation.