I have AP Racing 356mm 6 pots on my M3. They are awesome brakes, the stopping power is incredible. On a M3 it's a necessary upgrade if you drive the car hard, because the stock brakes are terrible. But on a Supra I personally wouldn't bother spending the 2k, the stock UK brakes are plenty good enough with OE discs and the right pads and decent fluid.
I also have the (brand new) AP 4 pot rears but I've never got round to fitting them. I don't have any problem with the brake balance.
I had 356mm KAD 6 pot brakes on my single Supra and standard uk rears, no problem there either.