The ER is excellent for the Lumin X1. The ideal placement would be right before the X1 using the 'B' side of the ER as the final connection to the X1. If you observe the A-side/B-side isolation needed avoiding mixing power supplies and cables, then the end result will be a wide open soundstage with excellent transparency. You can push it even further with the addition of an external clock but you will never know the difference until you try it and it sounds great without one. I use the ER with the X1 and highly recommend it.
Good luck finding an ER though as it is no longer in production.