I'm probably not your best guy for advice on this, since I've only fiddled with SDR and the panadapter just a little bit. You might be able to use the Icom 746 second receive antenna with an SDR dongle, and run that to your computer for a panadapter. I don't see the Yaesu working without tapping into the IF of the rig, which is harder to do. Maybe someone else can give you the details on how to do it with the 746, but neither of your rigs has an IF out, which is how the panadapters work. The SDR dongle is kind of a workaround, but I think it will work. Do a Google search and see what you come up with. There are a lot of sites out there that should at least get you started.
73,
Brett