Second post to keep things concise.
Are there still people here who can't get a Samsung SSD to work? I've got a 500 GB EVO and there were two things I had to do to get it rolling.
1. Install the latest, not publicly available version of emCore. I was getting panic errors on boot myself, until I patched this baby:
https://drive.google.com/file/d/0ByiOJ3RMUXDkekRxek5yempxUWs/view?usp=sharing
Got it from the emCore IRC, and as of this moment it's still the latest version (r967/968). Hope they think sharing it here is okay.
2. Get the Samsung 840 EVO fix:
http://www.anandtech.com/show/8617/samsung-releases-firmware-update-to-fix-the-ssd-840-evo-read-performance-bug
Someone here mentioned this earlier, so credits go to said person. My panic errors were gone, but playing a music file would always result in a freeze. At that moment I had to hook the EVO up to my PC anyway to restore a failed RAID array. After that very tedious process I flashed the firmware fix, and voila! It worked perfectly.