I'm pretty hyped right now because I finally managed to correctly get a hold of these kinds of archived. First encountered them in The Simpsons Game for PS3 and I was confused for quite some time back them and couldn't figure out how to correctly extract those ADPCM streams. I just sat down and thoroughly looked at those archives and the exa.snu header from other PS3 games. In the end it wasn't that hard to be honest (header information saved in a separate list in the header) but I'm actually quite proud of this achievement because back in the day, those archives were something like "the final boss".
I wanted to share my enthusiasm with you and provide the script.

Edit (2022-01-16): Updated for archives without CRC information.
Edit (2022-01-17): small error correction/style change