The USB adapter that comes with the Andrea mic is actually a 2-channel USB soundcard, as far as I can tell. So since you already are getting the better Roadie souncard, you can just discard the Andrea USB soundcard.
I plugged my Andrea mic into the Stereo Mic In port on the Roadie, and it works fine when testing with Sound Recorder. I Windows, I set the microphone volume very low in the Recording section of the Volume control panel, since the Andrea mic is very sensitive.
As for the radio, I think we're just out of luck until the SD team is able to get it working with external sound cards. I can't try the center line mono method since my G4 is already installed, but personally if it came down to that being the only way to do it, I would just revert to the internal soundcard and not use my amp.