What Center speaker are you using? Three 8Ks would be perfect.
I'm using a DSP5500HC, to my ears the height difference has been a constant issue, I physically tilted the speakers up a bit so that they are pointing right at my ears. This helped, but it never quite integrated well with the 8Ks, to me Trifield has always felt un-natural, to many variables, and the physical difference of the speakers makes it impossible to truly seamlessly integrate. So for critical listening Stereo is best (again, to my ears).
I agree this is all subjective and very psychological, but how can you expect a speaker like the 8K costing many times over what the D5K5 cost to work in harmony with one another? Though after the update I feel they play nicer together, I feel the only way to truly enjoy Trifield is to have the same speakers all around.
J