All the arc does is make the arrival time of the sound 'wave' reach your ear at the same time. If you have an external device to do this then your setup is less 'strict'

And Toe in of speakers is by manufacturer recomendation dependant upon the driver array and how close you are in the direct field. All toeing in of speakers does is make your listening area more in the direct field than the reverberant field.

Toeing in HT speakers really tightens up your sweet spot and it's really hard to to a larger room and get good sound everywhere when you do this. And I guess all the omnipolar speakers out there kinda make toeing in useless anyway.