The CDV line closely emulates an analog line. Technically, all faxes *should* be compatible with the CDV. I have however seen a couple not work, but this is *VERY VERY VERY* rare (generally old fax machines).
*in other words, there is no such "adapter"*
There is a list of known devices - Hitachi Omni Fax HF18TME is the only fax machine that im aware of.