I also had similar problems setting up my 990 with an adcom 7607, but i solved them.
First, would set up without the trigger and see if you can make the amp and preamp work without it.If it still doesnt work, then something is wrong with your connections or with the 990 (I am assuming your amp is working, though you did say your 750 died -fuses?)
If the amp/preamp works, then it might be the trigger cord. I bought a stereo one originally that would not transfer the trigger signal between my adcom 7607 and the 990.
If you are not very familiar with the controls that mught be part of your problem -- it was with me. Finally, i pressed the tuner button on the right of the second row from the top , then the video buttons bottom two rows to change from tuner to my inputs.
Hope this helps.