Mark,
Assuming that you are doing everything correctly, holding the bow verical and your form is rock solid repeatable and predictable, then I don't think adding more weight up front is going to help you much. It'll help some but not enough.
Now...there is one thing you might try before you go and buy different shafts. As mentioned earlier. Add the extra weight of front and see what happens. If they are still shooting stiff then place a small match stick or similar object shaved down to about 1/32-1/16 inch thick behind the side plate where the arrow comes in contact. This will in effect weaken the spine even more.
It just sounds to me that a 6-8 inch deflection between the fletched and unfletched is a lot. Also if you have some uncut shafts, try those as someone has already mentioned.
Hope this all makes sense and helps.