I tried to fully populate (16 each) HYS72T512920EFA-3S-C2 4GB on X7DBI+, but get no video. If I put only 15 DIMM, then system works OK. If I put 12x 4G and 4x 2GB(1D,2D,3D,4D memory slots), then system works fine as well. Is this a memory problem?
After changing "4GB PCI Hole Granularity" setting in BIOS from 256MB (default) to 1GB, system is able to boot up with sixteen 4GB 667 FB-DIMMs.