Understood, John. Sound cards connected to a RigPi USB ports will appear as available audio connections. Since RigPi supports external Winkeyers, your Modem keyers should work. This assumes all outputs from the Modems through their USB cables appear as separate devices, CAT, audio, keyers, in RigPi. You will need to switch the audio sources in RigPi manually depending on which one you want to use. Be sure to confirm that a special driver isn't necessary to separate the devices.
You are welcome!
--Howard