In case someone is interested to help with the RAM issue, here is the logs which show where the MRC is failing with the 16GB stick :
calling memory init function 2. calling memory init function 3. enter fcn_fffa78a0 calling memory init function 4. enter fcn_fffb8689 return from frag_fffc2026 with value 0x16 System Agent: Done. Sanity checking heap.
When everything goes fine, fcn_fffb8689 return 0x00, not 0x16