There is another workaround you could try, that i have detailed also, but you have to do it everytime you launch Cubasis (so it can be very annoying anyway) :
#1 : launch Cubasis with the Seinnheiser already connected
#2 : go to Audio Setup and enable Bluetooth / Airplay
#3 open the Bluetooth / Airplay devices list, select the iPhone/iPad , then select the Seinnheiser
#4 make changes to the Buffer Size to select a safe and correct value
#5 load your project again
Then the audio quality should be as expected, in my case this fixes the samplerate to 44.1khz.
To get 48khz i need to launch Cubasis with Audiobus…
I hope this will help 