I defer to Dan.... but I think you'll be OK:
Some of the earlier Z600 literature presented the Version 1 Z600 workstations topping out at 24GB. Here is from 2009:
http://h20331.www2.hp.com/Hpsub/downloads/Mini-WP_Z600_memory.pdf
My recollection is that Dan has explained that 8GB memory then was rare and very expensive, but if available it actually would work fine assuming it was of the proper type.
Later, in the era of the Version 2 Z600 workstations 8GB memory was not rare and much more affordable. At that time the Z600 literature started showing the max at 48GB. Here is from mid 2010:
I can see that the use of registered memory required the C2 version of the Northbridge chipset (which is a key hardware change from Version 1 to Version 2), but there is no mention that you'd need a C2 chipset (Version 2) to run 48GB total. But you do need to be running 2 processors to do that, which you are.
I'm feeling a little inadequate running my souped up V2 Z600 with only 24GB RAM........
