Don't know how helpful this will be, but I'm currently working on a Proliant 1850R, dual P3, SCSI drive array, etc. It's about 1 generation older than the boxes you all are playing with.
After erasing and configuring the system with the Compaq Smartstart CD and configuring the drive array (SmartArray 3200, 1 9-gig for the OS. 2 18 gigs in hardware RAID 1 for /home), I used the current Debian testing release candidate installer. It installed a stock 2.6.8something kernel, found the logical drives and detected all the hardware OK, etc, and basically worked, but only 1 CPU was alive. Debain uses grub by default, and that is working fine.
I then did apt-get install kernel-image-2.6.8-2-686-smp, rebooted, and both CPU's are running. The only issue remaining is a drive array problem that may be an issue with the Compaq drive array firmware and/or driver. (One of the RAID 1 pair is always wanting to do data recovery at bootup, does so, and then comes up with an amber indicator light and wants to recover again, but the Compaq Array Diagnostic Utility says all the hardware is good to go. the /home file system on that pair is functioning, but presumably only on 1 drive.) I'll be posting on that separately if I don't find an anwer.
If you're well and truly stumped, it may be worth trying the Debian installer on your box and seeing whether the issue goes away. Maybe the 2.8.6 series won't have the issue, or maybe the Debian stock testing kernels are compiled with the magic answer you're looking for.
FWIW,
doc