To install D2X-XL for Mac OS X, follow these steps:

• Copy the 'd2x-xl' application to your hard drive.
• Open the 'Support Files' folder, and copy 'SDL.framework' to '/Library/Frameworks/' or '~Library/Frameworks/', where '~' is your home folder.
• If desired, copy the 'd2x.ini' file from the 'Support Files' folder to a subfolder 'Config' the folder containing the 'd2x-xl' application.
• Create a folder named 'Data' in the folder where the 'd2x-xl' application resides.
• Copy Descent 1 and 2 data files to the newly created 'Data' folder.
• Download and extract d2x-xl-data-<version>.7z (e.g. d2x-xl-data-1.14.0.7z) to the 'Data' folder.

Regard that the subfolder names of the D2X-XL OS X installation have to start with a capital letter (e.g. 'Sounds2' or 'Textures').

Find a detailled Descent installation guide for OS X here.