check for offset on the amp outputs. if you have rail voltage on the output isolating coils, you have a shorted pair of output transistors. another common protection problem with Denons is bad power supply regulators. in some models, the +/-15V regulators had a habit of going south. if you find one of them bad, replace both. those are the most common problems. lesser common problems are a bad active filter transistor for the diff amp supply (looks like it's used as a regulator, but it's really an "amplified capacitor" or capacitance multiplier). this would cause 20-25V offset in all amp channels at the same time. or a bad main power transformer (the main clue on this one is no display when the unit turns on).
i wouldn't get too far into a 589, or any other 3-digit model, as they're the "low-end" Denon receivers. if it's not just a pair of outputs and the resistors around them that's bad for instance, then it's not really worth spending lots of time and money fixing.