Nice project! Not unlikely they used DSM-CC (https://en.wikipedia.org/wiki/DSM_CC
) as transport since it is a cable box. The VHS would not have picked that up but if there was a DTV PVR of the time, any brand, and the DSM-CC was embedded in the same mux as the recorded program you may be able to extract it. It is likely it is embedded since otherwise you'll need two or more tuner/demodulators to be able to download side band data such as software upgrades, EPG posters and apps. I have even worked on a case where they used it if for progressive download of VoD titles.... which is very stupid.
So there may be PVR harddisks out there containing videoway games. I have tools and access to expertise to check that if I am given DTV PVR recordings from then, let me know if I can help.
EDIT: The modem is used for interactivity, that was the normal setup.
EDIT2: Just realized, PVR was introduced 1999 by Tivo & co, so the only chance to find Videoway software this way is if it were broadcasted later than that and we find a really early PVR hdd... slim chance
EDIT3: Yeahh and it is analog but has embedded data, hence the data acquisition circuit. There were almost no standards for data transmission at the time so chances are it uses all kinds of tricks like using all over scan lines for data.
EDIT4: I just read the patent, seem that they used 4Mbps HDLC modulated over RF, so no need to store it locally then and no need to put it on the analog signal. Quite cool but unfortunately chances to find the data packets are ceasing to exist...