PPPoE and adsl are not mutually exclusive.
Most ADSL modems will will allow for the option of configuring with PPPoE - this is simply an authentication protocol (and a few other things) that lives on top of lower level traffic. There may be specific information that you need to get from your new service provider in order to complete the modem configuration so that it will sync properly with their DSLAMs.
PPPoE will not come into play until after you've established a layer 1/2 connectivity as it is being carried on top of the ATM traffic.
You will need to ensure that you have the VPI and VCI values configured correctly (these correlate with circuit information and must match details in the DSLAM config that you are connecting to on the ISP end).
In reality, that device is 4 devices in one. It is a modem that converts ATM to Ethernet (your actual DSL connection), a router (NAT/DHCP), a wireless access point and a switch (the physical RJ45 ports). Anything connected to it via the switch portion or the wireless access point portion will be able to utilize the DSL connection through the router portion.