Hello 
I’m using a UR22 with a MacBook Air (1.6 GHz Intel Core i5 and 4 GB 1333 MHz DDR3), and recording with GarageBand.
My issue is that I can’t change the sample rate (in Audio MIDI Setup) of my UR once GarageBand has been started, whenever I try to change it - it just goes back to 44kHz.
this appears to be a limitation of Garageband, and not your interface.
in regards to this, these are my references:
and
Thank you 