On https://www.ambx.com/beta you can get the latest amBX beta software.
When going to https://www.ambx.com/beta you need to register first. It will mostly take a day till amBX admins have verified your account and have given you the permission to login on the beta site.
The newest update at the moment is:
3.7.4 of the amBXFXGen.exe
Please find a beta release of 3.7.4 of the amBXFXGen.exe. This release was made especially to get Battlefield 3 working with the amBX system. Any feedback's greatly appreciated.