Actually, this is NOT a host-specific issue. I just updated my LTS host today and got the same problem there. If I go into GNOME's control panel's audio preferences, I have the choice between LFE-mono with Amplification or without amplification. That particular host has default PA settings. In that host's case, too, rolling back all PA packages to 1:1.1-0ubuntu4 solves it.
Actually, this is NOT a host-specific issue. I just updated my LTS host today and got the same problem there. If I go into GNOME's control panel's audio preferences, I have the choice between LFE-mono with Amplification or without amplification. That particular host has default PA settings. In that host's case, too, rolling back all PA packages to 1:1.1-0ubuntu4 solves it.