Tested on the radio: DAKY does not help, KY is refused whatever PC KEYING is set
to, and the "Serial port (DTR=CW / RTS=PTT)" engine on the second COM port keys
correctly. So my earlier "try DAKY first" was wrong, and the order is now the
other way round: name what works, mention the model that refuses.
The KY engine stays. It is documented for the FTDX101 / FT-991A / FT-710 family
and costs nothing to keep — a rig that refuses it now says so in one clear
sentence instead of transmitting nothing for no stated reason.