"The EAX API was designed around the DirectSound3D property set mechanism, and thus the EAX interface does not take full advantage of OpenAL's extension system, and EAX extensions all exist solely on PC."
"The Effects Extension (EFX) on the other hand, was designed specifically to provide a generic, cross-platform framework for adding advanced DSP effects to OpenAL. This framework offers the OpenAL programmer two new ways to process audio. Firstly, Sources can be processed through filters. Secondly, Auxiliary Effect Sends are introduced, so that effects processing can be applied to groups of Sources. The output of the Auxiliary Effects is fed into the final mix. It is also possible to filter Sources as they are fed into each Auxiliary Effect."
Wow, that's pretty contradictory, but it looks like OpenAL Soft supports it. Maybe software DSP (with possibly custom effects, like the XAPO stuff on Windows) would be possible. It seems software DSP is almost as fast as hardware DSP (and doesn't require hardware and drivers). FMOD (and by extension, Unity) use software DSP for their game audio engines.
I'm marking this 'wontfix', for the simple fact that there is absolutely no EAX/EFX on Mac OS X. OpenAL Soft does have EFX support, but we don't use OpenAL Soft on the Mac - we use Apple's native implementation instead.
The Mac version of OpenAL does have its own extension architecture, ASA, but it's not really comparable to EFX - it has much more limited functionality, and the API for creating things like reverb is different enough to likely render futile any attempt to create a Lua API that can handle both.