GRASS via Processing Toolbox doesn't work in QGIS 2.8.3 on Mac?

I am quite new to QGIS and working with the external applications such as GRASS.

When trying to launch a GRASS tool from the processing toolbox I get the following error:

Missing dependency. This algorithm cannot be run :-(
This algorithm requires GRASS to be run. Unfortunately, it seems that GRASS is not installed in your system, or it is not correctly configured to be used from QGIS Click here to know more about how to install and configure GRASS to be used with QGIS

When I am using GRASS from the Plugins menu it works. I have GRASS 6.4 installed to my system and running, GRASS 7 installed, but it doesn't run, probably due to some known El Capitan issue. Anyhow, GRASS 6.4 should be working. Moreover, there is also the GRASS that comes with the QGIS installation.

Unfortunately I messed up the path to GRASS that was originally set in Processing -> Options before I even tried if the original setup works. I tried really every possible path I could think of, to the GRASS-6.4 installation in my applications folder (/Applications/GRASS-6.4.app) and to the GRASS folder in the QGIS installation (/Applications/QGIS.app/Contents/MacOS/grass), I don't get the GRASS tools to working. I reinstalled QGIS to restore the original settings, but obviously I have to delete the particular settings before (but where?), because the path was still as I set it before reinstallation.

SAGA is working from the processing toolbox.

So, long story short:

1. Any suggestions what could be the issue? Anyone experiences with running GRASS via processing toolbox with QGIS 2.8 on El Capitan?


2. It would be already a great help if someone could give me the original path to GRASS set at "Processing" --> "Options"