How does the result with the tuning forks compare to what you'd get from balancing arrows at the base of the limbs (the sticky limb alignment post)? I'm curious as my fiberbow 6.3 (bought 2012) shows up straight using that method but always "feels" like the riser is pointing a different direction to the limbs.This morning I carried out the same procedure on my GMX riser. I aligned the string with the tiller bolt holes. I fitted the 'Tuning Forks' and immediately I could see the the string was perfectly aligned with all the riser holes and the tuning forks. So that indicates to me that the Fiberbow riser is not perfectly square in the limb pockets. In fact I inserted a shim of 0.8mm in both pockets to get the correct alignment.
I think the big advantage that 'Tuning Forks' have over Beiter Gauges (which I also have) is the fact that the string alignment is done away from the limb surface and nearer the string itself. This, as in my case, showed-up the riser pocket problem which the Beiter surface mounted gauges cannot.
I suspect that is as good as I could expect for a 'moulded' carbon fibre riser as opposed to an accurately machined metal one. But I still love shooting it!