One thing you have to watch out for with threshold panning rotation gates is sending the same stereo audio source to the 3:00 position on one channel and the 9:00 position on the other. This effectively cancels the audio by placing the same source 180 degrees out of phase with itself. It's generally better to go hard left and right when spreading the stereo field, there's less cancellation, but a by-product is that the source tends to appear a bit behind you in the sound field.
A little know fact about TPRG's (Behringer's "TPRG Pro" is a good example), is that thay actually determines gating function by averaging the degree's off-center of each panned channel, 12:00 being 0 degrees, then takes the highest and lowest amplitude of all sampled channels, and averages the two. If you have a stereo pair panned 9:00 & 3:00 the average of this cancelled signal and the highest signal of the other channel always results in 0. So your entire mix is effectivly gated...
Be careful which model and manufacturer you choose... I believe Manley makes a unit that does not use this averaging, but samples pan postion and amplitude on all eight tracks...