The memory I am using is of Qimonda manufacture which is included on the memory support list. I am sure, however, that the issue is not the memory itself but rather the DIMM slots. I have verified this by rotating the DDR through the various DIMM slots and, regardless of which stick I've used, the memory placed in CPU1 DIMMs 2 & 3 is not detected. I have tested this by populating each DIMM slot incrementally:
1) are you certain that your memory is all good?
2) are you only checking the memory quantity with the BIOS? Have you simply not bothered to boot into a 64bit linux? DON'T TRUST THE BIOS!!!
Try booting a 64 bit Linux LiveCD and open a terminal and type top
The top command will display detected memory and amount of RAM used.
At top of screen you should look for:
Statistics on memory usage, including total available memory, free memory, used memory, shared memory, and memory used for buffers. The display of memory information may be toggled by the m interactive command.
If the total available memory is around 32GB then you are good to go and the BIOS is wrong. If any other value other then 32GB then you might have a problem. Why not run memtest to check all the RAM to make sure you don't have a bad stick
As it turns out I did have a bad stick of DDR2 - I was not seeing it initially as I guess the stick was hosed enough that it would bring the entire bank down (and thus the adjacent stick would not register in the BIOS). I've since replaced the stick and everything is now hunky dory DDR2-wise.