Some success...maybe.
I searched for Yaobing's posts for references to HDHR, HD Homerun and I found references to enabling media network but for HDHR Prime. To be clear, I am using the original (old) white HD Homerun, not the PRIME, PLUS, or one of the other recent variants. In any case, I did try that suggestion and it made no difference. However in so doing I noticed my firewall was (quietly) blocking HDHR incoming communications despite that I had a MC rule set. Once I deleted the rule and recreated it, channels appeared during a scan. BUT...when I change the HDHR setup back to J River Media Center, it behaves just as it did before (no activity on HDHR tuners whatsoever). It seems I have to have the HDHR on "Other ATSC/QAM" setting for J River to even talk to it (more likely I suspect J River talks just fine since it doesn't know how the HDHR is set, but HDHR just ignores it's queries in this "mode" for whatever reason). So I guess the overall question of "how are you supposed to set this up?" remains...