"My amp is an ancient Carver TMF-25. still working fine. What really bothers me is the high background "hiss" noise level. I am pretty sure it's amp causing this and below are my options."
Try lowering the gain on whatever input you have your source plugged into on your 561. That may fix your problem.
Try lowering the gain on whatever input you have your source plugged into on your 561. That may fix your problem.