Many RME interfaces has pre-fader loopback, but not BF Pro FS. I don’t know what is the reason, but it would be great to have this option.
As a composer, I work a lot with multichannel sound projection and I do many sound transformations in the DAW. RME loopback feature is great to use for record many tracks to one without using buses, which could be in some cases problematic. It’s way easier. But with post-fader looback I have to set outpus to 0dbfs and the sound from loudspeakers is way to high.
I know, that maybe there is workaround, but it's not about doing it, it's about speed up your work.

Ideally looback could be switchable from pre- to post-fader.