That's a problem right there. I don't see an antenna selection box when I bring up the config. Is there a separate config item for the RSP1? I'm thinking that's what I'm seeing. One other question..... In the source dropdown box should there be separate listings for the RSP1 & 2.
Do you have this dll file, "ExtIO_SDRplay_RSP2.dll", installed in your SDR# folder? Are you using an earlier version of SDR# such as ver. 1361? All later versions are incompatible with SDRPlay.