I doubt the perfect chinchilla feed exists! As I understand you're interested in synthetic vitamin, mineral requirements. Please keep in mind that they are not as bioavailable as nutrients from plant sources. Organic/plant sources contain the intrinsic vitamin and mineral complexes, plants bond nutrient molecules to phytochemicals, amino acids, lipids. Synthetic vitamins and minerals are isolated components.
Pellets are actually designed to be supplemental. They contain lots of chemically synthesized nutrients due to inadequate ingredients (cheaper to make).
When choosing feeds with synthetic nutrients in mind, excess rather than a deficiency is more likely to be a problem. Not enough studies have been done to determine long term potential side effects, some potential toxicity issues are known.
Vitamin A requirements are about 6,000 - 10,000 UI/KG.
Tradition - 6,000 IU/KG
Nutrena nature wise 16% - 6,000 IU/KG
APD - 8,000 IU/KG
OXBOW 20,000 IU/KG
Mazuri 35,200 IU/KG
I know for rabbits the NRC recommends no more than 16,000. Liver becomes overloaded when excessive amounts are supplied. Unfortunately Oxbow can not explain why they decided to go with 20,000.
Selenium is an interesting element. It's recommended to add 0.05 ppm, although some feeds were used with no supplemental selenium and without any negative evidence. Most chinchilla feeds contain 0.2 - 0.3 ppm. Excess synthetic selenium predisposes to malocclusion. If you'd like to know how much selenium Oxbow has, please let me know. I should get results next week.
I noticed urine discoloration when chins consume mostly pellets or lots of pellets (body tries to eliminate synthetic nutrients). I know that the excretion of plant pigments can change urine color too, but I think in reality it does not happen that often. Maybe not all chins are effected by this and it probably depends on what else is consumed. I guess it's like with people, beeturia occurs in only about 12% - 14% of the population. And if it happens to you, you'll notice that it does not happen all the time, as it also depends on what else you ate and when you ate (acidity of the stomach). When I offer non-organic hays, I see urine discoloration more often, most likely because of the chemicals used (some fertilizes can cause urine discoloration too).
Chinchilla diet in the wild is diverse, they eat lots of herbaceous plants to get all the nutrients they need. Here are some plants they consume (with pictures

):
puya berteroniana
bridgesia incisifolia
pasto rey
pingo-pingo
oxalis carnosa
glandularia sulphurea,
moscharia pinnatifida
adiantum chilense
heliotropium stenophyllum
lobelia polyphylla
proustia cuneifolia
porlieria chilensis
lycium chilense
adesmia microphylla
astephanus geminiflorus
Chins in Las Chinchillas National Reservation especially enjoy
Berberis glomerata (blue berries)!
I try to offer a diverse diet: 12+ types/brands of hay (most of them are organic), apple wood and organic herbal supplement daily. I also mix blossoms, oat tops, roots, vita C (rose hips, hawthorn berries, hibiscus) with hay, my chins get a small amount of pellets.
If you're interested in some particular minerals/vitamins, please let us know. Hopefully someone else will reply too.