Pioneer SX 850 receiver Dolby adapter jack
I am awaiting deliver of my new (vintage) Pioneer SX 850 receiver and have a couple of related questions. This receiver has a "Dolby Adapter" jack on the back and according to the owner's manual, the dolby adapter is required when listening to FM stations broadcast in Dolby sound.
Here are my questions:
1. What percentage of FM stations broadcast in Dolby?
2. Is this adapter really needed and if so, what difference is there in sound quality?
3. If I need this, does anyone know where I can get one and what cost I should expect?
Thanks to all who read this and can give me a hand.