Hi,
These CPU's should work fine in your system I have 4 x 8389 CPU's in my DL585G2 system with 16GB of DDR2-667 and they work fine.
Are your CPU's known good cpu's? it could be that they are faulty.
I upgraded from 8216 cpu's then moved to 8384 cpu's which required a bios update to work but the move to 8389 cpu's was a straight drop in.
It could be a VRM issue, can you get me the p/n of your cpu vrm's so I can compare it to my vrm's?
Regards
Mark