Thanks a lot for your help!
I created /lib/udev/rules.d/91-pulseaudio.rules with the following content:
SUBSYSTEM!="sound", GOTO="pulseaudio1_end"
ACTION!="change", GOTO="pulseaudio1_end"
KERNEL!="card*", GOTO="pulseaudio1_end"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0424", ATTRS{idProduct}=="3fdd", ENV{PULSE_PROFILE_SET}="rme-fireface802.conf"
LABEL="pulseaudio1_end"
and `/usr/share/pulseaudio/alsa-mixer/profile-sets/rme-fireface802.conf ` with the content:
[General]
auto-profiles = yes
[Mapping analog-surround-51]
device-strings = hw:F80223718657:%f
channel-map = front-left,front-right,rear-left,rear-right,front-center,lfe
paths-output = analog-output
direction = output
[Profile output:analog-surround-51]
output-mappings = analog-surround-51
priority = 2
With these changes, the Fireface 802 is gone from the list of available PulseAudio devices.
How can I find out what the problem is?