I believe what Safeboot is trying to say is that the drive encryption itself is a symmetric encryption - i.e. the same key is used for encryption and decryption of the drive's content.
If using software encryption then MDE (McAfee Drive Encryption) 7.1.1 uses AES with 256 bit key to encrypt the drive content. As far as I know this cannot be modified by the administrator.
If using Opal encryption then encryption is performed by the drive itself which could differ between models.
The user authentication during the boot process is asymmetric meaning there's a use of public key and private key to unlock the actual drive encryption key and allow access to the drive content and the operating system to start.
Hope that helps :-)
Take a look at the MDE 7.1 product guide (available at https://kc.mcafee.com/resources/sites/MCAFEE/content/live/PRODUCT_DOCUMENTATION/24000/PD24867/en_US/...).
Search for table 4-22 (page 60) which lists one of the server policy options. It states that the "Algorithm" option "Specifies the algorithm AES-256-CBC for the software encryption."