The track to be replaced/doubled is highlighted (aka selected), then "drum replacement/doubling" is clicked under the tracks tabs (working from memory as I'm away from my mac). This track is analyzed, which can take a few seconds-minutes depending on the length of the track.
A dialog box appears that you can now set the drum's sound (snare, toms, others), select what drum sound you want (the samples are under the Media tab on the right-hand side of the screen).
Then click PRELISTEN, I'd recommend muting all the other tracks, including the one you're about to replace, so only the repalcement track is heard.
Now adjust your threshold, you should see yellow lines appear or disappear as you adjust the threshold. When the cursor rides over the yellow lines, the sample should be heard. Once you're satisfied with the threshold click ok, or whatever the button is called to execute your replacement/doubling settings.
Not trying to insult your abilities but try zooming in on the newly created midi track and see if there's data; maybe you are zoomed out too far to notice it. Or turn the volume up, check the mute button on the new track... Also, open the newly replacement track in the sample editor window at the bottom of the screen, select Piano Roll and see if there's data in there (little squares of different colors). Again, just trying to help.
Another way is checking YouTube for Logic 9 tutorials, Jonathan Something-or-Other had a few tutorials on Logic 9 and I believe Drum Replacement/Doubling is covered. It's where I first got aquainted with Logic, as I still consider myself new to the software.
I'm at work and away from my mac at the moment, I'll try messing around when I get home and try some replacement/doubling out. I'll be back on the HR forums tonight or tomorrow. Good luck!!