Frank, I think you can defeat the auto sound. I remember having to go into the menu to turn it on. I to like the Optimum mode because of it's added vibrancy but I find it a little too bright and seem to always come back to the pure mode. I am hoping when I get my display calibrated with the isf a/v modes I will pick up a little more brightness along with the accuracy of the pure a/v mode. From what I have been reading on this forum from those who have had this done this might be a reasonable expectation.