it's basically just another way to get signal from one unit to another. It's optical instead of analog so arguably better. It's also a single line instead of multiple RCAs.
You absolutely do not
need it. Analog RCA works just fine.
Here is a link that talks about this:
what-is-the-advantage-of-optical-toslink-over-rca-coaxial-cable
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2021 2SS A10 - Summit White - NPP - MRC - Adrenaline Red Interior Pkg - Black Appearance Pkg - Ground Effect Pkg - Suede Steering Wheel and shifter - Red Calipers - Carbon Flash Wheels w black lug nuts - DD Tinted Side Markers - Hero Tinted Rear Reflectors - Redline Fender Badges - 20% Tint
Audio System Build Log
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2014 Z/28 Summit White - sold 2020
2010 2SS/RS Summit White - sold 2014