I hate to quote myself, but I already answered that: For combo devices (specially ADSL), there are NO custom firmware images.
And of course, you can always check with
dd-wrt whether your device is supported.
If you desperately need custom firmware - get separate DSL modem (compatible with your ISP), and "cable" router (any one you like). You might also want to check whether your device can be switched into "Bridge" mode, shutting off the router part (and letting you to get your own router). And no, I am not going to check that for you.