Google for xw6400 technical and service manual..... that will have info on almost everything you'll need.
Search this forum for update BIOS from within BIOS. You get the .bin file from the unpacked DOS folder from the SoftPaq for the 2.38 bios, and you only put that on the thumb drive. Thumb drive goes in when the workstation is fully off, and you F10 into BIOS, and you look under the first column of BIOS and there will be the option then to use the USB drive as your source for the BIOS update. That should work, but you might have to clear the CMOS first.... look in the manual.
You'll also have the option in there to reset to defaults, and remember to save changes on the way out of BIOS.
You never know if an E5345 will work unless you try. It is not just based on the motherboard number. You always can try two of the fastest dual cores that HP ever certified for that workstationl..... the E5160. Latest sSpec for that is SLAG9. The reason I always recommend the latest sSpec version is that you get all the improvements Intel built into that processor, at no added cost. So, for the E5345 you want, ideally, the SLAEJ. The earlier ones should work. Start with one E5345 and if you can run 1 you will be able to run 2. I use Prime95 for my stress test on those..... it will show a processor failure quickly using that. It it will run that for 15 minutes you've got a motherboard that can run the E5345s fine.
