@ Memphiz
I appreciate your attentiveness and efforts in resolving SO MANY OSX-Kodi issues and realize that you've stated that working on the projectM issue is a low priority right now.
I just discovered something that may or may not help out.
I just installed OpenELEC (unofficial) v6.0.0 (Kodi Isengard v15.2)--which is Chewitt's effort to keep Kodi working with CrystalHD. I am running this on my ATV1 off a USB stick.
http://chewitt.openelec.tv/appletv/
ProjectM was not natively installed with this unofficial release; I needed to install it from the ELEC Media Center addon repo. After install projectM works flawlessly.
Maybe this info can help you resolve the projectM issue for OSX El Capitan on the other apple devices.
Thanks
Setup:
OSX Version 10.11.1
Platform MacMini 4.1 (mid 2010)
Processor Name: Intel Core 2 Duo
Processor Speed: 2.4 GHz
Number of Processors: 1
Total Number of Cores: 2
L2 Cache: 3 MB
Memory: 4 GB
Install Method dmg
Version of Kodi 15.2
Skin name Transparency 8.0.9
Other devices using Kodi:
MacBook Pro (mid 2014) OSX 10.11.1, Kodi 15.2
Retina iMac (5k, mid 2015) OSX 10.11.1, Kodi 15.2
ATV 1 OpenELEC (unofficial) v6.0.0 (Kodi Isengard v15.2)