You've got to understand the basic chemistry of brewing. Malted grains provide enzymes, extract syrups don't; perhaps more importantly, at boiling temperatures any and all enzymes are deactivated almost instantaneously. Also, just in case you are wondering: the rice and sorghum extracts we usually rely upon are about as sugar-rich as possible, because they are basically mashed in laboratory conditions with professional-grade enzymes. So if you threw some BRS or sorghum extract into a quinoa mash, the quinoa enzymes wouldn't likely pull any additional sugars out of the extract (and if they did, it would be by converting dextrins to sugars, which would decrease the body and residual sweetness of the beer...not a desirable outcome!). So to answer your original question: no, adding extract syrups to the boil will not somehow increase the amount of sugars extracted from your quinoa mash. They'll add their own sugars, and that's it.