cable connection

There might be no answer to this... but if you had  just one audio cable to upgrade , would it be between pre amp and amp or  pre amp and cd player.
Assuming interconnects are currently identical, then between CD and preamp (here the Linn principle would apply).
close score: . 6 for pre - source/  4 for pre-amp
I would go pre > amp. Like millercarbon said, then everything goes through your best pipe.
I will buy the cable to experiment, let my ears to decide where to put it.