Application is also crucial. I use the AC9SEMKII for my sub. The control, definition, ease of amplification and tonal accuracy improvements are quite notable.
I use a pair of 14SE MKII for my Sony 65z9d television, and my cable box. Wow what a picture difference, on what is arguably the best set on the mass market to begin with! (Only downside was the 65z9d is hardwired, so I had to cut the female end off the pangea and strip it down to connect...but that is no fault of the pangea). 3d depth perception of the picture is enhanced significantly. Smooth Color saturation is slightly improved, and fluid motion is also improved. At under $300 for 2 chords, my viewing experience on a $5k set is enhanced considerably.