Well this AGW packet engine incorporates some audio to data decoder. So basically you either need to reverse engineer that and code it again, or interface with it if it has an API.
It's a bit surprising that there is some audio in the chain though. You use the audio input of the PC ?
I'd rather consider to leave that audio decoding system alone and replace the receiver by a better documented 433 receiver to either an arduino or USB, if you know the format/protocol of teh messages. If not, replace the sender as well by another 433 sending device (paired with the receiver).