Like Ken says toe-in is dependent on the situation. One of the best ways I know of to find the right toe-in is to sit in the sweet spot while someone else adjusts the speakers while you listen. However, this still has it’s problems since different tracks can sound better or worse than others with the same amount of toe-in. Also if you are adjusting for multiple seating this doesn’t account for the effects on the other seats.
One way to start is listen with no toe-in at all. Then point the speakers straight at you. While listening have someone change the angle of the speakers and find the place in between where you most like how the front soundstage sounds.
Also be aware that what sounds best for 2ch might not sound the best with multi-channel. And if you are using DSP to convert 2ch to multi-channel you might also want to play around with the DSP setting for the width and depth of the front soundstage.
Sorry just to many variables for a simple answer.
