You did not state what the size the RAM modules are and that may make a big difference. Also the specs call for RAM no faster than 3200 which also may be part of the problem though the RAM you have should run at 3200...depending on the size of the RAM. Also this service manual page shows which slots the RAM should be installed in.
I recently purchased the Corsair Vengeance 3600Mhz memory (there was a weird sale and it was the cheapest option) and tried installing in my R8.  I can get the system to post with 1 module installed, but once the other unit is in, I am not able to.  Is this a lost cause?  Will I need to return the memory for another option?
Corsair Vengeance 3600 possible to install in an R8?