As far as I know, the WCG200 is a Cable Gateway and is not compatible with your ADSL2+ Broadband. The AG401 on the other hand, is only for ADSL connection. Not suitable for ADSL2+ as well.
Linksys have the X series ADSL2+ Gateways (X2000, X3000 or X3500). You should check them out and inquire your ISP for compatibility.
Links:
X2000 - http://support.linksys.com/en-apac/support/gateways/X2000
X3000 - http://support.linksys.com/en-apac/support/gateways/X3000
X3500 - http://support.linksys.com/en-apac/support/gateways/X3500
Hope it helps.