On the mac I've also found that Keka on the mac (downloadable from mac app store for £4.99) also extracts the .exe file.
You have to run it twice:
1. First time run it and a couple of subfolders appear and within one of them another .exe file.
2. Run Keka again on the newly extracted .exe and the files appear.
Hope this helps.
How to convert ChessBase Mega/Big Database on a Mac
Moderators: Watchman, Mark Uniacke, mrudolf
Re: How to convert ChessBase Mega/Big Database on a Mac
I can confirm that the app Alexander mentioned successfully extracted the EXE! Thank you so much.