PMA450
PS Engineering has an alternative to the GMA350.
The new PMA450 uses a patent licensed from the Wright Patterson Airforce Base (USAF Battlefield Audio Group) that invented Multitalker for their Air Force pilots. While we name it IntelliAudio, it is exactly the same the USAF uses.
What they did was to allow pilots to place Com 1 and Com 2 in 9 unique positions within the stereo headsets. It allows the pilot to take advantage of what we call "The Cocktail Party Effect". For example, say you are at a party with your wife (or husband) and they are talking to you when you hear your boss' voice and.....he has just mentioned your name. Surprisingly, you are able to "tune out" your spouse and pay attention to your boss and whether or not you are going to get that raise.
It really does work that way! The big difference between GARMIN's 3D and IntelliAudio is that it does not change how the intercom works and IntelliAudio allows you to place the radios into positions that are best suited for you.
So this dimensional stuff really works, but the implementation is what distinguishes good from great.
Hope this helps.
Mark Scheuer