Just out of curiousity, I searched for Technics and some other brands that do not have their own forums already, looking only in thread titles, since 1/1/14.
Technics 168 thread titles
Denon 61
Luxman 43
Panasonic 9
I couldn't think of any other big ones that don't already have their own forums. Obviously Technics made a LOT of gear that is discussed quite often at AK. If one was to base it solely on this, Technics might warrant a forum. But it's not, of course.