I don't know about the Panasonic, but the Eclipse has 8V outputs. I had the 8053 w/ 8V outputs connected to an amplifier that had a "maximum" input voltage of 1.5V with the gain set to minimum.....and I had to really be jamming on it to drive it into clipping.
That Sundown has a pretty wide swing on the input sensitivity...up to 6V. Depending on your listening habits, musical content and other settings (bass boost, etc) you would probably be fine with it set a little higher than you have now with music. Just be careful if you're blasting test tones at a loud volume. If you don't have access to a DMM listen carefully for distortion/etc for a while.....or just run to Radio Shack and grab one of the $10 cheapies.