Another good way is using Audiosnap.
Enable Audiosnap, go through and make sure the transients are where you want them to be (detection can be a little iffy sometimes), and then click the Copy as MIDI button on the Audiosnap palette.
Paste that into a new MIDI track routed to Addictive Drums and you're set. Works great.
EDIT: Ah, sorry - I misread! I read that as you wanted to add an Addictive Drums snare sample to an existing audio track. Disregard! (But hey, this might be useful for someone else right?

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