This is just me, but if you aren't having any issues with Backdrafts with the furnace, I wouldn't worry about a fresh air kit. There are alot of mixed thoughts on these. Is your heat from your woodfurnace going into the cool side of the central furnace? I guess I don't understand. If the woodfurnace is in the basement, I would build a box around the blower and duct a large return on the floor up ahead. And by adding a filter, you clean your air, and get better circulation in the home. Having the blower drawing the air from your basement could cause negative pressure. If you duct that up above, you eliminate that pressure in the basement with the woodfurnace. Then your heat will go out the ducts in the home, and that Cold air return will help your heat travel though the home better. Eliminating the need for an OAK. Now if your heated air does go through the return of the central furnace, I would change that.