Hi Peter,
the first question isn't easily answered:
there is no direct NMEA from Catalyst or TMM as the default way on Android are mock locations.
So Androids mock locations and location extras provide similar information and more compared to NMEA (details like currently used geodetic frame are not available in NMEA afaik).
On the other side the SDK does provide NMEA output - and you could enable NMEA output (GGA, GST, the default stuff) and retrieve the corresponding events - parse the event (string) and funnel it to your own NMEA driver.
But the amount of work is in no relation to the benefit.
Plus not even sure if it makes sense at all.
So the most simplest way would most likely be Androids location API plus location extras. Details on the content can be found in both SDK-Developer and TMM-Developer documentation.
On the second topic - this is a system USB event - and can be captured by any software.
I'll check on the explicit implementation in TerraFlex - I assume are referring to the 'you just plugged in a Catalyst antenna - do you wanna switch?' message, right (loosely translated).
Regards
Nico