The problem with ADSL routers, is that there is seldom publicly available information for the ADSL chips themselves. The ones that have been rewritten have been done by reverse engineering firmwares (which isn't an easy task) or by hardware means i.e. logic sniffers etc...
Both of which take a lot of time, and if you don't have the equipment both money and more time to learn how logic probing works.
Have you opened the unit up at all?
