Got it working! Memory is now showing 1600!!!
I upgraded the BIOS (after a fair amount of reading...) from 1.12 to 1.17.
Strange thing. Before the BIOS upgrade, I couldn't actual edit the XMP to enabled in the BIOS settings. Depending on the boot, it would be set on its own to Disabled or Enabled. Didn't make a difference though, as the memory was always showing 1333. It was a read-only setting.
After upgrade, I was able to freely edit it. Did so, and the memory is now 1600 in CPU-Z!
Thank you very much for your help!!