I asked Slacker directly to check from logs the stream format my car pulled, and they said my car with standard audio requested an AACv2 at 40kbps stream. The stream sounded terrible, which is why I asked in the first place. They assured me that the stream format was entirely at the request of whatever device you are using, and is not stored anywhere that can be shared between devices. If you check the Android app it won't reflect the setting you chose in the web player.
I have a standard audio car, so the high bitrate option at the login screen doesn't exist for me. I lost the ability to play reasonable quality audio from the Streaming app in the car with the 8.0 release. I've started streaming Slacker from my phone over bluetooth. It sounds far better than the crap the car is willing to play directly. I'll never forgive Tesla for crippling my streaming audio, those jerks.