Most DSL modems, even when set for external PPPoE, will hand out a 192.168.x.x address by DHCP, so that you can easily view modem status and change modem settings. However, you can't access the Internet by this path. If the OBi got such an address, the "direct to modem" test was not meaningful.
Please post both modem make/model, router make/model, and any special settings you have configured in either.