It is possible as these work off of SIP to begin with but there are no MSO's doing it this way they want to only provide dial tone to the customer and beyond the D-Marc is the customers problem. So all you can do is take the analog ports and connect to a PSTN and convert them to rj45 that way in what ever protocol you need.
This is CABL.com posting #332969. Tiny Link: cabl.co/mbyMD