In should really ask Michael but saw your post here.
In the manual for the preamp the general preset description states "This program provides you with the color and tone of the 160A at a threshold of """ and a ratio of """, using "" Kernels of distortion."
I assume this to mean to choose the appropriate preamp to the comp in order to get the 'correct' emu chosen.
I didn't see one listed for the Medium comp so I used that one because the Ratio was the same. Not sure how much it matters using different pre-amps for different comp settings.
^ah ok. makes sense. i use the threshold, ratio and whether or not i select an "over" (soft knee) program as guides for selecting the appropriate preamp. but as always, it comes down to what sounds right to you.