how to remove double nat scenario?

[NickLacey]

My ISP supplied modem/router is crap. I have a Western Digital N900 wireless gigabit router, and would like to use it as my network controller, and relegate the existing modem/router to being an ADSL2+ modem only, (using PPOE Relay?)
however, currently I am experiencing issues I attribute to the double nat situation created by running 2 routers, since I cannot set my modem to bridge mode; it uses PPPoA, and my WD N900 only has options for PPoE

 

[Emerald]

have you tried assigning a static IP to the WD router and then place that IP into the DMZ of the modem/router?

What model mode/router is it?