The transponder accepts ADS-B format but not ADS-B+.
The SkyView and D6 do not accept either ADS-B format. They use NMEA or Aviation format data.
Garmin is not a real nice player in this corner of the market- the ADS-B and ADS-B+ formats are proprietary with no documentation, so they must be reverse engineered. Garmin has not publicly stated what the difference between ADS-B and ADS-B+ formats are, so there's no obvious reason to use ADS-B+ over ADS-B.
What are you trying to do with this data in our various systems? All the Garmin devices that can output ADS-B data have at least 4 serial ports so you can get Aviation out at the same time.