You are completely right watercrayfish. When I first bought this plant I looked around on google and I found a lot of threads of people not being able to grow it and killing it, I was amazed because my setup is not great by any means.
Here is how I have been able to grow it:
Substrate: Potting soil
Liquid ferts: Potassium sulfate after weekly water change. Seachem Flourish Comprehensive after each water change and other 1-2 times between water changes. Potassium nitrate 2-3 times between water changes. (I have a giant clump of hornwort so I need nitrates, I will stop dosing when I stock more heavily the tank)
Light: This is where it gets funny, a desktop lamp is what Im using lol! It is a CFL bulb, 18 Watts and 1200 lumens (I dont know PAR), it does come with a reflector which I guess helps.
CO2: DIY CO2. The recipe I use is 1/2 teaspoon of yeast and 400 gr of sugar. I think the difussion method with DIY CO2 is even more important so I bought the cheapest powerhead I saw to difusse the co2.
I have pics of the mother stem but it is embarrasing as the seller gave me the crappiest stem he could find, the lower leafs had algae and some leafs had holes and stuff. The baby stem is planted now and leafs are finding their way altough some are still tangled. When it grows I will post a pic of it. My ammania gracilis is by no means as cool as the ones you see on google, I am able to grow it decently well, no crippled leafs or anything but when you compare it with the ammanias of the pros it is lacking color (it turn greenish with a pinch of orange).