Mark, welcome. Despite the lengthy discussion, there doesn't seem to be anything specific said about how you calibrated the sub level. Whether you let YPAO do it, which should be fine, or did it manually, there's a possibility that the 2600 sub out isn't putting enough voltage into the EP500 amp to keep it "awake". My own EP500 level setting was about 7 o'clock after calibration(you have yours around 9), which made my receiver put out more voltage than if the sub's level control was set higher. Try calibrating with the sub level control around 6-7.
