Apple devices default to AAC at 44.1kHz, standard for AirPlay.
In order to transmit Hi-Res via Bluetooth up to 96kHz (limited by the Bluetooth standard) you need to use a Hi-Res Bluetooth transmitter connected via USB to your device, then connect Bluetooth to the Hi-Res transmitter.
Alternatively you can connect the GO blu directly to your device with a USB-to-Lightning cable for up to 96kHz capability.
