My friends Nathaniel, Charlie and I figured out a better way to map rex files into Logic using EXS 24 instead of Ultrabeat:
-Create a new EXS 24 instrument, open EXS 24 and click on edit.
-Click on Instrument > Recycle Convert > Slice Loop and Add Samples to Current Instrument.
Now everything’s automatically mapped to the keys. That’s way easier and you don’t have to deal with audio slices in your arrange window. There’s one bug where the slices start in the right place but end at the end of the whole loop, but that’s only if you keep holding down the key. Meh.
-Use Instrument > Save as to save the instrument as something else to be able to access it in other projects.
If you want to hear the original loop, you can export the rex file as MIDI in reason and import the midi file into logic and assign it to that instrument. If you’ve remixed the rex in reason, exporting the whole song and then assigning that midi track to the new instrument will work. Logic also automatically assigns instruments to your other tracks, so importing whole songs from Reason is pretty easy!
The method of dragging the rex loop into an audio track still works well if you don’t need the slices mapped to the keys. In both methods, changing the tempo will have the loop stretch to match (either as slices in a folder or as MIDI data triggering slices).