Hm, so you want to put the stream data itself in there? Above 60 kHz (and probably below - say - 85, otherwise I think most sound cards will be problematic, not sure how high you can really go because I have never tested it).
I might be interested, but I fear that doing something like this will take a lot of time (which I don't have - I could potentially hire someone for it but then we really need to be talking about a LOT of stations), and chances are that the company that's doing this now won't give out the details needed to implement it. Also all the info that I can find is at least 5 years old, and what Wikipedia says (that it's compatible with HD) can't be true because HD is broadcast using a completely different mechanism - the best possible thing would be that radio's that can receive HD can also receive this signal but I really doubt that.
What would your goal be? That normal listeners can tune in to this extra signal? Or do you want to send audio to stores etc. similar to the analog SCA channels? If so it might be a lot easier to keep things analog! If - instead of the (standard) 7 kHz wide SCA signal, you would use 60-75 kHz (15 kHz of audio, AM mono single sideband encoded with a synchronization signal) things would be much simpler.
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My objective is to also build an FM reciever that is capable of decoding the AAC streams
Decoding the stream isn't the issue, but you would also need to be able to convert the audio signal to bits, which is more problematic - that's probably the issue that this VuCast solves.