Substituting quinoa flour for wheat flour in egg pasta

I don't know why About.com warns that "additional protein will increase toughness" when the whole purpose of adding corn starch is to reduce the protein.

All purpose flour should have around 10% protein and 90% starch. Pastry flour has 8% protein and 92% starch. Cornstarch has 0% protein. You only have to mix cornstarch and all-purpose flour in the mathematically correct ratio to get a mixture which behaves like pastry flour in terms of protein toughening.

The numbers above are rounded, but then, different manufacturers will produce flours with different percentage of proteins, and some wheat proteins also get tougher than others depending on the cultivar, and recipes still work with that kind of tolerance. So I use them and mix 80 g AP flour and 20 g cornstarch for every 100 g pastry flour I need, which results in a flour mixture with roughly 8% protein content. I use it primarily for flaky crusts, and it works quite well there.

I have used quinoa flour in various recipe and it would have a similar effect as the brown rice flour, though its taste would differ. I would recommend against substituting it (at least not 1:1) for the tapioca flour as that is likely working as a kind of binding agent to some extent. Experimentation may yield different results based on the ratio, but also tapioca has less flavor (which may be ideal as a balance).