I think one of the Radioactive@home users made an app some years back that worked with the GMC320 and they shared it via email. However the user disappeared and requests on that site have been unanswered.
I recommend radmon.org for a nice world map. At the moment there appears to be a server issue related to a recent hack, but it has been reliable and active for some years now.
A user at Radioactiveathome has recently posted a link to a copy of the software that reportedly works with the GMC300. It may also work with the 320 Plus. See www.radioactiveathome.org/boinc/forum_index.php and search for GMC300, then click on the message# to see the post.