Well let me start by saying this, first PPPOE is not supported by A400,A800..etc.
Honestly I can not remember how I did this in the past, to install A800 unit where a speedtouch was in the network All I can say here is if you need to assign the fixed IP address in the tenor:
Conf unit 1
ip (type the fixed address)
If I remember more about speedtouch I will let u know