Mac Tools?

[Andross]

I play the Linux version of Amnesia. For the level editor though, which requires some of the Windows dlls, I additionally purchased the Windows version and can now use the editor (as well as play the game^^) via Wine, which Cedega is a fork of.
As there exists a Mac version of Wine, the same might work for you. Also, buying the game a second time is much cheaper than a new PC.