1. People use acids to extract alkaloids including tryptamines from plant material all the time. This is well known hard-fact chemistry.
2. An empty stomach is not just sitting around with a pool of strong acid in it. That is a common uneducated misconception. Acids are VERY costly in terms of energy and materials for the body to synthesize, so that would be a waste, and also damaging to the stomach and intestine. They are only released AS NEEDED by ingestion of food containing calories needing digestion. A few grams of shrooms, taken on an otherwise empty stomach for better absorption reasons, are not enough to trigger significant digestive acid release. Hence soaking_in/consuming_with a strong acid like OJ *will* improve extraction of the tryptamines.
3. Yes, Phenethylamines, both amphetamine compounds, methyhlone etc, as well as 2-C drugs are all INHIBITED in absorption as well as EXCRETED FASTER in the presence of acids. Also well known scientific pharmacology, NOT anecdotal (there are often warning stickers on prescription amphetamines that juice and other acids will make them weaker, antacids will make them stronger. But its hard to get enough taking chewable TUMS tabs... one teaspoon on baking soda exactly 10 minutes on an empty stomach prior to methylone will increase potency by about 1/3 I have found... although it seems to have the side effect of total-water emissions out the other end a couple hours later, unfortunately, so I tend not to do it.