Toomanyknots, I'm quite puzzled as to why you have 'brittle' or weak white oak and hickory. These two woods are about THE best woods in tension! Of course there can always be one board that is just iffy due to fungus or what else. But it appears you've used several boards, from various suppliers, all without any positive effects? I'm sorry to say this mate but it sounds like it could be a problem YOU are creating! Hickory and oak are difficult to mess up for a lumber yard. Especially in the USA, close to the source, the wood should be properly handled and properly dried.
Could you post a few pictures maybe? One of the end grain so we can see the rings, and one of the face of the board. Perhaps the grain isn't as straight as you thought? Perhaps it has some discoloration that could be due to fungus? I don't know, but I'm having a hard time believing that you bought weak wood in several occasions with several species and several suppliers. How did you determine the wood to be weak, low density and brittle? Try to make a simple selfbow / boardbow first and rule out several things. Do a bend test and measure the SG accurately. Measure temperature and humidity of the room where you store the wood to rule out a less than perfect MC of the wood.