Hi Bob,
Just to clear a few things up. Your problem can be one of two things:
1) Your centre sphere (front or back or both) may be flat and hence no bounce.
2) The electrovalve on the centre sphere may not be opening.
Both would lead to a harsh ride.
More analysis would be required to determine which one it is. Since you've already bought your spheres then you will be able to determine the fault by a process of elimination.
If it turns out to be the spheres then you've replaced them and that will be the end of the matter. However, as I suspect, it is the latter problem especially if it seems that it is intermittent. Search on electrovalves and suspension ecus in this forum to find posts explaining the problem. The freewheel diodes in the electrovalve coils burn out causing the 'transistors' (dont shoot me for the vocabulary) inthe ecu to overheat and fail. It starts intermitently at first gradually getting worse until theres no soft mode at all.
Not sure on your size question. I'm not at home at the moment so can't look up the manual until Sunday at the earliest. Can anyone else look up the suspension section and find the sphere volumes for Bob?
When you look at the neck of your new spheres you won't see any orifices (dampers) at all. Thats because they are built in to the electrovalve unlike wheel spheres. Although the orifice sizes are larger in the middle sphere compared to the wheel spheres its not by much in relative terms.
As to your question on comfort/stiffness/roll they are all controlled by the same mechanism. They are not really differentiated. Any of the measured parameters will trigger the hard mode if the parameter exceeds the set limit. The response is the same no matter what caused it.
The front sphere is no more difficult to replace than the rear. A Pleiades tool is best because the sphere is very close to the chassis and only the thin band of the Pleiades tool can slip through the gap.
Hope that solves some of your confusion at least. Please let us know how you get on.
Cheers
noz