AptioMemoryFix.efi cannot be used with any slide boot flag. In principle the version implemented in my original EFI-Folder distribution should work. Sometimes it is necessary to reflash the BIOS or reformat the boot drive to prevent memory allocation errors. Also enabling "Above 4G decoding" in your BIOS settings might help to prevent memory allocation errors.
The version of AptioMemoryFix.efi I have does accept slide arguments. The one in your folder did not work, I tried everything. The only way to boot macOS, the first time, on this mobo was to use this version of AptioMemoryFix with slide=129 (calculated from memmap). After this first boot, I had to remove the slide argument. Maybe now the one in your folder would work.
I had several random boot failure after that, but not related to mem alloc. One was because of a APFS problem that was solved by booting to Recovery and reinstall last APFS snapshot. Booting single user mode and fsck was possible, and fsck did not found anything, but I could not boot farther. Anyway, that wa solved.
The MSI X99A XPower AC I have is not as good as the Asus X99 Deluxe, as I could OC the 5820K CPU to 4.7 GHz and memory to 2.75 GHz (specs being 2,7 GHz). Now, I can only OC up to 4 GHz and mem does not even reach its specs (stable at 2.17 GHz). At least I am able to run my gig, but I miss my Asus stability. However, the BIOS is cleaner on MSI, and I have native NVRAM (was not working on the Asus).
One other problem is that the on board wifi on the MSI is an Intel 7260, unsupported by macOS. The module is set in a proprietary slot on the mobo, but inside the module, it is simply a M2 Key A+E card. In the Asus module from my dead mobo, the module had a mPCIe slot going directly on the mobo by the I/O shield. I bought a mPCIe to M2 A+E adapter and hopefully will be able to install the Broadcom card (that I know works with macOS) into the MSI instead of the Intel one.
EDIT: Wifi + BT works perfectly! Tricked the MSI to use the Asus Broadcom module.
One other strange thing, my previous gold 1 kW PSU that I thought was dead) is working fine with the MSI card. Would not work with Asus Z170 when I tried. Asus X99 Deluxe and Z170A are ATX while MSI X99A is EATX (and has more power connectors on the mobo), maybe that is why.
I have the MSI USB map done (did not do a limited 15 yet).