I was mainly curious if lifting the front stage higher using these channels in conjunction with the derived overheads would make any difference, particularly sounds leaving from the front to the back and back to the front that would make it to the overheads.
I hung presence speakers on the wall behind and wide left and right of fronts 20 inches below the ceiling at the same position as the side surrounds slightly angled in. The I set the DSP-1 to presence with a 20ms delay.
What I found that it does make a difference in some sounds transitioning from front to overhead or overhead to front, like the thunder in Underworld Evolution, some of the RPG launches in The Kingdom or the big ship fly over or the big explosion when the landed ship explodes right at you in Starwars episode two. It seems to smooth out the transitions of some of the sounds make them sound more like they were naturally placed higher.
As good as it is though I would not probably not go out of my way to purchase something just to give me presence channels with this mix. However if one were to in order to gain some smoother transitions with overheads then I would get two units and have one use the front left and right for the front presence mix and the second use the rear left and right for the rear presence mix to lift the rear sound as well.
Next thing I want to test is lowering the sound stage using a wedge type speakers on the floor like mentioned a few posts up to see what if any difference it makes.