Our R720 only recognizes 384GB RAM of 512GB installed when using 32GB Quad Ranked LRDIMMs

We are trying to upgrade the memory in our R720 server (8x 3.5 Bays/2x 8-Core I-Xeon E5-2670 2.6GHz, Raid H310) with 16 sticks of 32GB RAM modules.

We install the16 sticks (512GB) according to Dell guidelines on http://www.dell.com/support/article/us/en/04/SLN153646 (so no sticks in the green slots).

Issue:

The BIOS only acknowledge 384GB of 512GB installed.

The DRAC only acknowledge 8 sticks, 256GB, and adds that another 4 sticks are without values.

We do not get any kind of error messages and we have tried the sticks.

Our memory type is SNPF1G9D/32G 32GB DDR3L-1600 LRDIMM. This memory is low voltage and Quad Ranked.

On the above Dell Memory Guidelines it says three things that make me wonder if we have purchased the wrong memory:

1. "Up to two QR DIMMs ... may be populated per channel.LRDIMM" - How can we populate the last slot in every channel if we have used QR memory in the previous two?

2. "low voltage (1.35 V), which supports speeds up to 1333MHz" and not 1600 like ours.

3. "Max RAM: LRDIMMs Up to 768GB (PowerEdge R720XD with 2.5 inch hard-drive configuration)" -  The paranthesis makes me wonder what the max for LRDIMMS is for our R720?

Questions:

What can we do to use the full memory capacity of our server?

What memory can we add or substitute to reach the max capacity of our server?

(I have a Service request number.)