indeed, AES is another digital format. while AES > S/PDIF will usually work without a special converter box, I doubt it'd work the other way around. That's because the voltage for an AES signal is ~5V, while the voltage for an S/PDIF signal is 0.5V. So if you send an S/PDIF signal into something that is expecting an AES signal, it won't be able to read it because the voltage is too low.
The Hosa CDL-313 will convert a coax S/PDIF stream to AES.
the Hosa ODL-312 will convert an optical S/PDIF to AES.
one of those boxes isn't too much and might be useful for you.