This is the ReCycle file format for both Mac and PC platforms generated internally in Reason Essentials (see “Bounce Clip to REX Loop”) or by ReCycle version 2.0. One of the differences between the original REX format and REX2, is that the REX2 format supports stereo files.
Unlike the Dr. Rex device, Dr. Octo Rex can also load and save the device panel settings in a special Patch format (.drex). The REX file(s) and the Dr. Octo Rex panel settings are also saved in the Song file just like every other patch in the song.