Once again: On the AMD64 platform, RAM is none of the chipset's business. THE RAM CONTROLLER IS IN THE PROCESSOR, and its capabilities remain the same regardless of what chipset you use.
Registered DIMMs are required and used on Opteron platform (socket-940), which also happens to like ECC RAM. So you should opt for a 940 board rather than a 939 - because the latter was specifically made to support unbuffered non-ECC RAM.