This is a pair of EL-8X “Distressor” units. The “Image Link” works best when you have two units in need of linking. One of the beautiful parts of Empirical Labs products is their consistency! You can pick up these units as pairs, or get one now and a second years down the road and they will link and lock perfectly!!
Image Link gives the EL-8X an additional capability when using two units in stereo. The original EL-8 employed a rather unique “summing and phase detection” method to achieve stereo lock, and while this added a “thickening” component, it was not always the best complement when an engineer wanted to maintain an absolute “left/right” balance at all times.
The Image Link takes a more traditional approach to locking two units in stereo so the “left/right image” will hold true. Additionally, you can combine the two settings to gain a 3rd and absolutely unique to the Distressor capability. This capability combines the phase related aspect of the original link function with the additional “Image Link” function for perfect “left / right” balance in addition to the “thickening” factor created by the original circuit.