Because the library makes use of ultrasound, it requires the sample rate higher than 38kHz. The RapidEars library forces the AudioSession to 16kHz which is far less than the requirement..
And I think sub-sampling from 48kHz to 16kHz is quite easy (only skip 2 & 3 bytes). By supporting this feature RapidEars can also work well with other framework like AirPlay. I think it is valuable to implement.