I want to add in here some important bits of info I've recently found out via Slacker support.
In the 8.0 firmware Tesla removed the high bitrate feed option from all cars with the base audio package. There is no way to make your base audio car play directly from Slacker a stream which will not make your ears bleed. I asked them to pull logs from when my car was playing, and the format the car requested was AACv2 40kbps! No wonder this sounds so bad to so many people!
The web player's setting is completely independent of the car. The car picks the format it wants and indicates it to the stream as a query parameter to the stream url. There is no cross-device quality setting. If you install the Android app you'll have to enable the high quality feed setting there too. There is absolutely no link between the web player and the car. That was never the case.
If you are unsure whether your car is playing back a decent stream or not, email
[email protected] and ask them to check from log data. Give them the email address of your Slacker account and a time range when you were listening in your car. Be polite - they're nice people. If you are unhappy with the crippling of the Slacker stream in your base audio car, email
[email protected] and give them an earful.
I'm now playing my station from my Android phone via Bluetooth. It sounds so much better than the built-in car functionality. No ear blood anywhere!