What inputs are you using on the PM-16?

From a quick google search it doesn't appear to have dedicated power amp inputs (if that's incorrect you have another problem but this info still be useful).

If not and you are connecting the SR6004 pre-amp output to a CD/Tape/Tuner/etc. input you may be causing yourself grief.

Try connecting the tape loop or VCR outputs on the SR6004 to the inputs on the PM16s' tape loop. I have no experience using an AVR like this but I used to have 3 stereos each on a different floor of my house connected this way with no problems.