Hi cwchce,
Sorry for not being more responsive recently; life got in the way. I have a couple of followup suggestions/questions that will hopefully move you in the right direction.
1) What kind of Mac did you tell MultiBeast to pretend your Customac is (iMac, Mac Pro, Mac mini)? My setting for this motherboard and my processor is MacPro 3,1 (this is in the 'Customization>System Definitions part of MultiBeast; I've read that 4,1 and 5,1 are unstable). This is important (and I guess I forgot to mention this earlier) because you can tell your computer to pretend to be any kind of Mac you want, but doing so affects the functionality of your computer (not to mention I only know my BIOS & MultiBeast settings work for the system definition I used). You can check your definition by going to the Apple Menu then clicking 'About this Mac' then 'More info...' then 'System Report.' The 'Hardware' option on the left hand side of the window should be highlighted by default and the first and second bits of information in the window on the right should be Model Name (which for me is 'Mac Pro') and Model Identifier (for me 'MacPro3,1'). If you have your system definition set to something else you can always change it by re-running MultiBeast in Safe Mode and selecting MacPro 3,1 in the System Definitions part of MultiBeast.
2) I noticed the number in the 'key' field for 'device-properties' has some spaces in it when I think it's supposed to be one very long, continuous string of characters. I don't know if that's an artifact of copy-pasting into your post (or from my post if that's where you got it). I would check your boot.plist file and make sure it is in fact one long string of characters (remove the spaces).
3) If you use that string for the 'key' field following 'device properties' did you make sure you have the correct amount of memory dedicated to graphics. For that string the amount of video dedicated to integrated graphics has to be 32mb IN THE BIOS or it won't work.
I hope these help. I'll try to check back more frequently. We'll get your Customac humming along yet!