Sprout100 and DSD File Playing Via Bluetooth

Hi there…

I have started playing around with DSD files and trying to understand if or how resolution is affected if I play a DSD 128 file on my iPhone (via a program called ST-1 PRO).
Is that signal still coming in to the Sprout at 24 bits? Will it play at a sample rate of 128 or will it be downgraded because I am connecting to the DAC via Bluetooth.
Do I have to connect to the Sprout via USB in order to get that full sample rate?
Thanks! Learning so much about new audio formats since entering the wonderful world of Sprout.