Okay... Sorry... Forget what I just wrote... Seems to be my 20 to 51 solution with the mentioned LADSPA Low Pass Filter. "default" device is just playing fine.
my .asoundrc: pcm.xfi { type hw card 0 channels 6 }
ctl.xfi { type hw card 0 }
pcm.ch51dup { slave.pcm "plug:lowpass51" slave.channels 6 type route ttable.0.0 1 ttable.1.1 1 ttable.0.2 1 ttable.1.3 1 ttable.0.4 0.5 ttable.1.4 0.5 ttable.0.5 1 ttable.1.5 1 }
pcm.lowpass51 { type ladspa slave.pcm default path "/usr/lib/ladspa" plugins { 0 { id 1098 # Identity (Audio) (1098/identity_audio) policy duplicate input.bindings.0 "Input"; output.bindings.0 "Output"; }
1 { id 1672 policy none input.bindings.5 "Input"; output.bindings.5 "Output"; input { controls [ 120 2 ] } } } }