To me, David experimented on a shit ton of spores before finding a way to cross breed goo or spores with some other form of material such as a spider of some sort, then probably through that evolution, he managed to cross breed it with something larger making it a morpher of some kind (this resulted in an egg). Nobody can pin point the exact process but we saw mosquitoes involved with his experiment. You can also bet that he had viles of the goo (which to me was a liquid version of the spores that has the ability to morph things rapidly).
Spores= Impregnation of a Host with a life-form.
Goo= Morphing of the Host into something genetically different.
My best guess is the mural in Prometheus gave away the process. That is, dipping a neomorph in goo to make an egg.
Being impregnated by the facehugger meant getting an xeno and depending on the planet, would result in an organic looking xenomorph. If in the harshest environment, it will result in a more bio-mechanic HR Gigertype xeno.
David helped evolution along, i don't think he would be the father of xenos, that term sounds trite. He was merely scientifically experimenting.