I used to work on Denons. The relay you hear may not be for external
devices it may be the protection relay on your speaker line. If you
look at the main amp at the heatsink you should see both channels
(mirror image). In between the P and N outputs there should be two
large low ohm (less then 1 ohm) resistors (sometimes in a single 3 leg
pkg) where the pos & neg signal converge. There should be zero DC volts
at this point (spkr out) there is a DC sense off of the current
limiting resistors and any DC voltage at this point will cause the
relay to trip. Usually if the fault is major taking out the outputs you
will have your rail voltage (+ - 40-80V) and the relay will hault any
passage. If the relay is chattering it could be that you have a small
amout of DC leaking into the line. I would look at the beginning of the
amp around the differential transistors. These can be individual
transistors or a pair in a single 5 leg pkg. Usually they are together
as thermals effect the way they work.