Hi,
I happen to have some experience in this matter. Here is how I made it work:
1. Determine the connectors needed. For the 970 the 12V trigger output uses a 3.5mm mono plug.
2. Figure out the type of connector that is required by your AVR. There are several kinds. This is the hard part. Keep in mind, that some connectors are color coded. So if you are fortunate then the color at the back of the AVR will tell you the connector type.
3. Now, walk over to the nearest radioshack and buy:
a. Adaptaplug wire.
b. A 3.5mm mono connector for the 970. This is also made by Adaptaplug
c. Appropriate connector for the AVR. Made by Adaptaplug. You just want the connector, no wire.
d. A multi-meter, if you don't have one.

Now you have a cable when you connect (a), (b) & (c) together. They plug in quite easily. This will be the cable. But we still don't know the polarities.

Now, comes the interesting part. The multi-meter. This can be used to determine the polarities. The tip will give you +12V from the 970. You will have to determine what the AVR needs. My manual told me that the tip of the AMP had to be +12V. So I verified that with the multimeter. Then I plugged it in.
Now, whenever you turn-on the 970, everything should wake up.

-Sandeep