Dumb q. does the existing controller that works on the 741 will work on the 821s?
Yes. As far as everyone has been saying, it can control both models.
My question would be can one controller be used for both when both are connected. For example if I have two 741's in one usb port can I connect two 821's in another usb port. Would be nice if this could work I woulndt have to buy another controller.
Also if the price is above 3.5K I don't think I will purchase a 821. Thats almost 4k once you factor in a power supply and possible controller.
I'm pretty sure you could run 721s and 741s on the same controller, you just had to be careful when updating the firmware because it was different for them.