Let's see. The thread is over 2 years olf, the people the originally responded may not even be members anymore, and your question is not related to the original question.
On top of all that, your question was ambigious.
Do you mean, "Can the Sound Blaster external card be used to listen to streamed audio if hooked up to the internet"
The short answer is yes.
The longer answer is that the Sound Blaster external card doesn't care what the sound source is, it is used to convert computer audio into speaker signals. So, if you use some program (Windws Media Player, etc..) to listen to streamed audio from the internet, the SB external card will indeed convert it to speaker signals, and then you can listen to it, provided you have compatible speakers.
However, you have the problem of how you are going to get a reliable higher bandwidth internet connection to your carPC, along with other problems.
You may want to research this CarPC thing a bit more before you go off and ask random questions.