Ya, I thought that was pretty generic so added the pic. That was easier than trying to describe it more fully. Words are really not my friend anymore as it is getting tougher and tougher to write something legible. Regarding springs on poppet valves - I understand that CC has different springs for tuning the double barrels, but they are not readily available. Had a discussion with S4 last year regarding this when they updated and rebuilt the CCDB on the dh bike. No idea if Fox offered any different spring rates for the old DHX2.Without the image you also just described a shim stack. The only real difference is that shims make it easier to tune the spring rate and progression. "Poppet valve" suspension manufacturers rarely offer different spring rates so you are stuck with adjusting preload.
Shim stacks are much lighter so should react faster. This could make a difference for high frequency chatter but no idea how that relates to bikes. I did talk to a guy who tuned race cars and he explained how a straight shim stack could give the same dyno results as a tapered one, but on the track the tapered one had better cornering traction. I assumed it was the lighter stack being able to react quicker. If you can think of things in the frequency domain, less phase shift.