Also, did you buy a matched 64 gb set, or did you buy two 32gb sets or something else? 

Have you tried disabling XMP (it may down clock the frequency to 2933 if it works though) 

Did you try disabling XMP and seeing if it posts with 64gb @2933? 

I am about to try this and will respond, promptly.  As a follow up question; will the machine run faster/better with 64gb at 2933, or with 48gb at 3200?  I am a massive multitasker with many rendering/gaming/recording operations going on at once.

While solely gaming, will games run faster with the 48gb, because they are using only 8 and amping off the 3200mhz, whereas the machine will only start to see benefits if I use over 48gb of RAM at once, or will the games run faster with the 64gb of 2933mhz?

Thank you for your help.

For gaming I would say that the 48 gb @ 3200, everything else being equal, would be better (although the difference probably wouldn't be noticeable for most intents and purposes).  I doubt you would need more than 48gb solely for gaming, or even 32 for that matter, and having more RAM than needed will not result in a performance improvement.  It only makes a real difference when you're utilizing all the available RAM.   If you're using a significant of RAM for other purposes, then probably it would be better to have 64 gb (the max supported by this board).  

Can you point me to the place where you figured out the R9 cannot handle 64gb of 3200mhz RAM?  I need to send this proof to Dell customer support because they keep telling me it can handle it.

I have switched the cards around into all the slots to test.  All of the slots work, as well as all of the cards.

if 3 of the 4 work and you can use each one at a time in slot 1 then the 4th slot is physically bad.

Here's what I found for R7:

https://www.dell.com/community/Alienware-Desktops/Aurora-R7-HyperX-Fury-2933-problem/m-p/6054291#M2876

It's the 2933 though.

I tried disabling XMP and it would reset them to 2400MHz.  However, when shutting down and inserting the 4th card, it would still not start (same 4-yellow flash memory error).  I put them in, individually, to set them all to XMP-Off, but Alienware seemed to keep resetting them to XMP-On after new card insertion.

I have not been able to find a way to put all 4 in and set it to XMP-Off, because the machine won't boot into the BIOS with 4 of them plugged in.

I'm having exactly the same problem...

Honest mistake or scam? 

I'm not certain if it was just luck or what but I had zero issues upgrading my machine today.  After reading this thread, I was concerned that I'd have issues.

Today I installed (4) 16GB Corsair 3200 sticks, turned on the machine, waited for about 3 minutes before BIOS kicked in, and shazam, all good.

The BIOS automatically picked up all of the RAM, recognized the 3200 speed, enabled XMP, and set the voltage to 1.35.  I literally did nothing but insert the sticks and turn the machine on.

I've just posted a message about the newest BIOS stopping my 3200 64GB RAM working. It worked perfectly up to that point. Does your PC have BIOS 1.0.7?

I think you should try it again as after the Bios update to the R7 in June, I was successful at running two 16GB HyperX Fury Dimms at 3200 Mhz and they are still working fine as 18 July 2020.