Ha, not sure what I was doing this morning but I count get it to extract from an audio file. I've just gone back to try it with another audio file and your right, it works with the transients.
The work flow thing is what I've been used to doing in Ableton, I could hit "Command+I" to accept the warp markers then group/highlight the ones I don't need to move the audio around, I can see the workflow in Logic works the other way to add them in then move then move them in relation to each other.
Anyway, no problem really the main thing was to extract grooves from audio, I'm not sure how I missed that earlier. Cheers