If none of the above work and you can't detect a voltage at the outputs then it could be that an internal component failure has tripped the DC protection circuit. If DC is detected in the output signal it is shunted to ground to protect your speakers.
Help with hookup
Inherited some audio equipment. Hooking up a McIntosh mc2300 preamp to a McIntosh mc352 amp to a pair of Acoustic Zen Adagio speakers, but I don't get sound out of the speakers. I can hear when I plug in the headphones, so there is that. Any ideas?