SteadyClock FS is a different topic. It is there to lock and sync quick and reliable if ADI-2 DAC FS is clock slave and the master is connected via ADAT or SPDIF.
More information see:
- https://www.rme-audio.de/de_steadyclock-fs.html
- https://www.youtube.com/watch?v=Ti0aHW-zYcs

Background: a few features have been removed from the ADI-2 DAC FS, to be able to get the price below €1000.
At least this was the initial goal before corona and delivery chain problems and last recent price increases.
Now the price increased to €1199 (around €200 more). With SRC, it would be even pricier.

Additionally, I think SRC makes most sense if you have multiple digital inputs and outputs (e.g., AES, ADAT, SPDIF).

This to support, i.e., the following typical connection scenario:

DAT recorder, with fix sample rate, no word clock, thus needs to be clock-master.
But you want to record in 44.1 or double or quad speed.
Then the DAT recorder can be clock master, additionally decoupled from the system's clock master.

          Clock       Clock
          Master     Slave (of UFX III)
          @88.2      @88.2
PC----UFXIII---AES----> ADI-2 Pro FS
                  \<-AES------  "
                          coax SPDIF
                           SRC (48<->88.2)
                             ^
                             |
                     DAT Clock Master @48 kHz

Same if you want to connect e.g., a guitar modeler via ADAT or SPDIF.

A solution for you is to have two different config profiles for your ADI-2 DAC FS which you can even map to keys on the device or on the remote. Create a 2nd profile where the ADI-2 DAC FS is clock slave and getting the clock from the digital port to which your BT receiver is connected to.

Easy to setup and handle by using the new ADI-2 Remote ....