Usually needs to be enabled for IP Softphone on the station form. Otherwise, the DMCC part is pretty straightforward. if you can 'stat aes c' and 'stat aes i' and 'stat aes l' and everything's up, then you're good from CM to AES
Frequently, 3rd party application vendors use Avaya's DMCC and TSAPI SDKs installed on their Windows servers and have their application hook in to those. To say as an exmaple, when AES's demo cert expired in January, to install the SMGR authority cert in a call recorder, I just had to go into c:\Avaya\tsapi SDK\certs or something and paste in the contents of the SMGR CA cert into 'trustedCAs.pem'
They usually have some configuration be it by text file or gui to tell the application how to connect up to AES. Perhaps it's requiring secure connections?