flip default for enable filter to be disable filter to work around settings bug

There's some kind of a bug in the domain-server's settings file handling where if you have a "checkbox" style setting with a default value of TRUE, you can't set it to false...

To work around this problem I'm changing the audio mixer "enable/disable filter" to use a "disable" wording, and making it's default setting FALSE...  This has the SAME "BEHAVIOR" for default behavior, the box will now be default UNCHECKED -- so that the filter is NOT DISABLED --- i.e. ENABLED.

To DISABLE the filter -- you can now check the box and it is disabled.

This allows for testing of behavior with the filter enabled or disabled.