Yes  good  point  John 

With this  ''not selected'' it's  not possible to route  audio  from  a  app  running  on 
say  sdr &  fire fox  to data  app  , vara ,  fldigi  etc  using the  internal  audio routing 

Selecting , allows the  windows  mixer to  be  selected as  audio  in 

Then  there  is  a  listen to this  device option, which if  activated  caused  [on my]  win10 set up  
something  like a ' wem copicat'  effect , loop round  delayed  audio 
feed  back ..all for  free  ..

Applicable to System audio  , as opposed to  device  audio -?

73- Graham