Any help for a ReplayTV (5040) user hooking up to mini box?

I have an admittedly ancient ReplayTV unit, two actually that up till now worked fine of the coax cable from the wall. Now that Cox is going all digital in my area, I have to figure out how to connect to the blasted mini box. I've tried connecting cable from wall to mini box, coax to the Replay, then coax to the tv from Replay out, and while I can see the new digital feed with the Replay off (indicating signal flow through) as soon as I turn the Replay on I get snow for a signal. In setup I would like to switch the Replay input from cable service without a cable box to either digital or analog cable box, but the it requires an IR code, and Evolution DMS2344 is not listed. Tried calling customer support, and they had not heard of ReplayTV (older than Tivo) nor were they able to provide an IR blaster code.  Is there any hope? My DVR with lifetime service will be a doorstop shortly if I can't get this connected.