The PS Engineering models(6000,
7000, etc.) mute music under both conditions.

Just a small correction, while it is true that the PMA6000 will mute the music
during both intercom and radio activity, the PMA7000 series has a dedicated
front panel switch labeled "ICS". Its function is to allow the pilot to select
whether radio and intercom mutes the music or elect to activate the karaoke
mode.
It is the karaoke mode that I use most often, otherwise, the music continously
plays and mutes, plays and mutes.......a scenario which could prove to be
frustrating.
Mark Scheuer
PS Engineering, Inc.