@12-13, that's true -- if a hacker is truly determined, they can get at the sounds. But you can't just apply strait-up AES-256 to anything. You need to specify the cipher mode. AES-256-GCM is the best out there, and plus, 256-bit AES is top secret U.S. government secrets. Though you should probably layer the encryption twice or thrice, or even compress the encrypted sounds. Could someone get at them? Yes. But not in a very practical timeframe. So far, AES-256-GCM has not been broken since its inception in 2007. That's quite a long timeframe. You could always do what I do with networking data to encrypt it... though I won't give out any specifics. Let's just say, lots of encoding and encryption and other things, if I choose to add more. But I think that sound library makers know that if you're given enough time and power, you can break encryption. What they mean by "no one can get access to them" is that no one can reasonably get access to them; that is, no one would ever be willing to spend the time and effort to break a high-level encryption algorithm like AES192/AES-256 just to get at a few game sounds.
Also, about the loading thing. You'd be surprised that mainstreams gamers are quite used to, and will play your game a lot more, if your game has short-to medium loading phases, and its really good. They won't mind he wait. You encrypt all your sounds and it takes 30 seconds just to load a map? Fine, will still play if its good enough. But the reason people like Ironcross and I push so strongly to not use BGT is because it literally takes me about 30 minutes to extract the sounds from a game. The equivalent in password security would be a 4-character password (aaaa, bbbb, cccc, ...) with hardly any password dictionaries in use and trying to break the password with a website that throttles you to 100 password guesses per hour. Its harder if you pack the sounds into the executable but its definitely possible; the header your looking for is SFPv (note the casing).
"On two occasions I have been asked [by members of Parliament!]: 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out ?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question." — Charles Babbage.