Compiling Cores to add for RetroPlayer

I want to load the Dolphin, ParallelN64 and Reicast cores that are missing from RetroPlayer in LibreELEC beta 9 versions. I have a 64bit PC, so don't have any hardware limitations. These cores worked in Lakka, and the LE Remix build looks to have dolphin. I know parallel should work if dolphin does.. can anyone help get these to work?

Is this Lakka process the same for compiling cores into LibreELEC? http://www.lakka.tv/doc/packaging-a-libretro-core-for-lakka/

Can someone help translate this into working with RetroPlayer?

The cores are GitHub - libretro/parallel-n64: Optimized/rewritten Nintendo 64 emulator made specifically for Libretro. Originally based on Mupen64 Plus. GitHub - libretro/reicast-emulator: Reicast is a multiplatform Sega Dreamcast emulator GitHub - libretro/dolphin: Dolphin is a GameCube / Wii emulator, allowing you to play games for these two platforms on PC with improvements.

I guess I'm missing the link on why all the cores work in Libretro.. Anyway, do you know how to package 'add-ons' for installing - say I just wanted Moonlight, or Chrome added on to the LE 9.0 beta OS - are there any how to's I can follow to get there.

I rather keep the gaming as much as integrated into LibreELEC/Kodi as I can with the RetroPlayer.. Unless, in the LE 9.0 Remix, would Retroarch/Emulationstation open cleanly/integrated - or is it like a whole other GUI that opens and 'shuts down' LibreELEC/Kodi?