already have 846's because someday i'll move to quad.
no response from Tyan.
has anyone here done this?

hmmm...i don't see a reason why it shouldn't work.
The only difference between the Opteron 2xx and 8xx is that the 8xx-series have one additional coherent Hypertransport-link.
Since an Opteron 2xx wil work just fine in a Uniprocessor(Single-CPU) motherboard, i guess an Opteron 8xx will work in a dual-CPU board without problems.

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The opinions expressed above do not represent those of Advanced Micro Devices or any of their affiliates.

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QUOTE The only difference between the Opteron 2xx and 8xx is that the 8xx-series have one additional coherent Hypertransport-link.

Minor correction:
- The Opteron 2xx has three HT links, one of which is coherent.
- The Opteron 8xx has three HT links, all three of which are coherent

As to the original question, in general, it should work...The BIOS and Kernel Developer's Guide for AMD Athlon™ 64 and AMD Opteron™ Processors' ">http://www.amd.com/us-en/asset...nd_tech_docs/26094.PDF :

QUOTE During POST, the BIOS checks the multiprocessing capability of AMD Opteron™ processors, and configures the system accordingly.
Multiprocessing capability detection is not required in a UP system.
All processors must be DP capable or MP capable in a DP system. If any processor is only UP capable, the BIOS must configure the BSP as a UP processor, and must not initialize the AP.
All processors must be MP capable in an MP system. If any processor is not MP capable, the BIOS must configure the BSP as a UP processor, and must not initialize APs. If all processors do not have adequate multiprocessing capability for a DP or anMP system, the BIOS
must display the following message:
*********** Warning: non-MP Processor ***********
The processor(s) installed in your system are not multiprocessing capable. Now
your system will halt.
If all processors have adequate multiprocessing capability for a DP or an MP system, but have different model numbers or operate at different frequencies, the BIOS can do one of the following:
• configure the BSP as a UP processor, not initialize APs, and display a message indicating that processors with different model numbers or maximum frequencies have been installed, or
• implement the algorithm defined in “Processors With Different Revisions or Maximum Frequencies in Multiprocessor Systems”.

So it should work, but whether it works correctly on a particular Tyan MB and BIOS revision is hard to tell