I am sorry, I have been a McIntosh dealer for quite a few years and they have never offered a double din to the general public....in any location..Japan, Korea, Canada, USA...no where. This headunit is the product of McIntosh, but is not a stacked 406...since a stacked 406 doesn't exist, we will try this:
McIntosh made this a double din due to the needs of the Subaru Legacy. The second din is to make way for a cassette player. The tech at McIntosh is correct in saying this. It might have 4 rca's out, but we don't see that picture showing it. But, you are correct in saying that it is not available to the public...ie...you can't go into a McIntosh store and order one....not here nor even in Japan. This was like the Mark Levison system in the Lexus, the Dynaudio system in the Volkswagen, and the Bose system in everything else. McIntosh has only made one Headunit that was specifically designed for the Subaru Legacy.
McIntosh has installed one of their headunits, an amp, and their speakers in only one other car from the factory....the Ford GT. That HU is the 406...but for 150,000 dollars, it seems logical that they would put their top head unit in it. Not in a 30,000 dollar family car.