More command line options are needed:
-O Loopback:0,0 -V -2 -U
Make sure you see an entry in the log file that says "audio device:
Loopback:0,0" or whatever alsa device you are using.
In reality you're probably better off making sure op25 plays audio through the default
device before you worry about getting it going through the loopback.
As a secondary recommendation, the alsa buffering is considerably better in the version of
sockaudio.py found in my github repo. I suggest you upgrade to that version as it has
other fixes too.
Graham