I have never tried Amaranth please let me know how it works out. Here is an attachment I sent someone else for GF brewing. Hopefully it will help you. At the end is a cheap easy way of malting grains and roasting. Remember to malt you must have the seeds (husk). Make sure your grain and yeast are gluten free. With sorghum syrup you can use unmalted grains.
I have Celiac Disease and brew strictly gluten free. My goal is strong hopped dark beer which I always achieve. My gluten free beer is awesome. I have successfully malted Buckwheat and Quinoa grains. I use the red quinoa instead of the white because it adds more color to the beer. I use Red Quinoa (Ancient Harvest or Bobs red mill white quinoa) and both are gluten free. As for buckwheat, you canNOT use Kasha or de-hulled buckwheat. You need to use buckwheat seed with the husk. Make sure that the buckwheat is gluten free. Many brands of buckwheat are cross contaminated with gluten. I buy in 25 lb bags from the Birkett Mills.
The Birkett Mills: America's #1 Producer of Buckwheat Products they have a phone number on their website. They are not expensive (about $25 and you only need about 1-2 lbs per batch).
I use the malted quinoa for flavor -- it smells sooo sweet when steeping like tea at 156 degrees prior to the boil. I use buckwheat more for color but flavor as well. The buckwheat really adds dark color. buckwheat adds lots of flavor as well but it is not as sweet as the quinoa. It is more bitter and nutty but adds fantastic depth and color to the beer. I would suggest 1 lb malted quinoa and 1/2 to 1 lb of buckwheat per 5 gallon batch. I use many other grains for color and flavor but I do NOT malt them. these include Sorghum grain, millet and buckwheat and quinoa as well. Just roast to desired color and grind. If you brew with Sorghum syrup, you don't need malted grains. Any grains will give color and flavor. You must roast all grain prior to brewing. I always use Sorghum Extract and/or Rice syrup for my base and add about 2 lbs of grain to the brew. The syrups have the sugar and enzymes needed so it allows you to add unmalted grains if you want to .
Here is my process: I usually malt 2 lbs at a time.
I take a large piece of soft black window screen. tie it into a sack with wire and pour in the grain. I submerge the grain in a bucket of cool water for about 12 hours. I change the water once or twice. after the 12 hours, I rinse the grain and put it back in the bucket and put a towel over the top. This helps keep molds out but also keeps the moisture in. I take the grain out and rinse it about every 8 hours throughout the malting. After 1 or 2 days, you will see the seed sprout. When the rootlets are 1.5 times the length of the seed you are done. I take pizza pans and lay a towel on them. I spread the grain on the towels to dray-- usually about a day. then I take the grain off of the towels and spread on the pizza pans to dry 1 or 2 more days. The thinner you spread it the quicker it drys. A fan may speed up the process as well.I then bake the grain in the oven starting at 170 deg F. after 1 hour I increase the temp to about 225, and turn it up 25 deg about every 1/2 hour. The darker you roast the darker and more bitter the beer. be careful, it will start to smoke up a bit at temps above 375deg. I have even roasted at 400 deg charring it like black coffee and the beer was a bit bitter but was a great color and with sorghum syrup and a ****load of hops it was great beer. after cooking, cool and place grain in a paper bag for at least 1 week to allow the bad flavors to escape. Grind and brew. When brewing the grain you do not want the temp to get over 165 deg F. at higher temps the husk will release bitter tannins into the beer. Have fun. I just brewed two batches today.