I contacted Proscend regarding the VPI/VCI settings for the 180-T and was told unequivocally that the device does not support ADSL. I found this very strange as the data sheet does have the ADSL2+ specifications, so I asked for clarification and was again told that they do not have any devices that support ADSL.
This was Proscend's "Marketing & Sales Director" so one would think he would be able to talk authoritatively about the capabilities of his products. My guess is that they have quietly withdrawn this feature. At any rate I'm not deploying CPE devices in a mode that isn't supported by the manufacturer so it looks like we're back to no options for ADSL.