The princible toxins in yew are in the wood but arent very soluble in water, hence why you can drink out yew bowls and eat with yew chopsticks, but a dog chewing a stick can die. I wouldnt drink vodka that had sat for week in a yew cup personally.
The chicken of the woods question I quite simply dont know. I would eat it, but i wouldnt feed it to my kids until the next day. The toxins in yew aren't acculmative, they cause heart and TNS issues quite quickly after consumption. If yew grown COTW turned up while teaching, it would go on the firmly in the suspect pile, with full explianation. Chicken of the woods is an iffy anyway as it gives a good number of people bad guts and allergic reactions. It feeds by breaking down the wood it is growing on what else crosses with that I dont know. Sorry cant be more help.
The source of COTW growing on taxus been "lethal" appears to be the author micheal jordan. i cant find any referance to any actual poisoning due to taxus through eating COTW. 6 journalists got sick at MJ's book launch form eating COTW coincidantly. There doesn't appear to be much solid evidance of taxine crossing into the fungi, however COTW does cause problems in it self.
Clear as mud!!!
edit chichona alkaloids [quinine etc] cross over from the tree into staghorn fungi.