Chromecast audio ships with a 3.5 mm stereo cable. However, the device supports RCA and Optical input as well. For those who are looking for official accessories to use Chromecast Audio with these inputs, Google Store now has these two in stock.
The official help center article says:
Chromecast Audio works right out-of-the-box with your existing speaker systems that have an aux input or line input. Chromecast Audio also works on systems with RCA inputs and optical digital inputs. Note: RCA and optical cables are not included with your Chromecast Audio.
RCA Cable for Chromecast Audio
This cable is a commonly available retrofit cable that converts the stereo analog output from Chromecast Audio into a stereo RCA connection. You can buy this here. The price? $15.
Optical Cable for Chromecast Audio
If you have a speaker with Optical Digital input, this is the accessory you should buy (if you are looking for the official accessory that is). You can buy the Optical Cable for $15 from here.
So, who’s buying these?