Glad to hear that you got it resolved.
I removed the mainboard from the server last night, just to have the case ready when the new one arrives and i noticed that the part number of the mainboard is : 410426-001 which is the first revision.
According to the spare parts list (http://h20566.www2.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-c00751484&sp4ts.oid=89018) , this mainboard's description is "System board (used no eariler Dual-Core only processor systems)" , while the one i ordered, and the one i have in my other system are P/N: 436718-001 which is the "new" version that supports newer CPUs.
The first revision boards will not support dual quads (at least the 5335 i have) whatever the BIOS version.. I updated the BIOS to the latest (2008.10.27) and the lights-Out 100 Remote Management (2.12) and still the issue remains.
So, yes.. you need the latest BIOS version, but will only work with the newer boards..
I don't think they care actually.. what's in it for them? ;)