i am not sure i totally agree with digitalsmigital in the matter....and i aint trying to start a flame war.
so here goes my thinking.
i can record onto any one of the 4 tracks direct, play back that track and record on the next one. What i mean is i can record a drum track onto ch 1, then play it back and listen to it while recording a bass guitar track onto 2 direct. SO, the 4 record heads do not necessarily engage all 4 at a time.
the thing to consider is that the BUSS mix always goes onto 1 (left) and 2 (right). so if you did use the buss, 1 direct and 2 direct have to be out!.
i think you could assign 1 and 2 to buss, and also 5/6 to buss. these 4 chanels would then be mixed onto tape channel 1 & 2.
then record 3 & 4 direct. you would have to hard pan stuff to keep it just on the one buss btw
wont promise that, but i think you can.
hey. shouldn't blow anything up if you try it anyway.