Page 8 of the 7700's manual touches on this process (just so you know we're not doing anything crazy here). The old Model 750 manual (Outlaw's original multichannel amp) says something similar and even mentions a specific Radio Shack part number, but that number no longer works. Instead, I did a couple searches at RadioShack.com. I don't know if there's an easier "all-in-one" solution than what I found at Radio Shack, but this will work. Here's what I found.

First, get an AC adapter like this one , and then get a 3.5mm "type F" Adaptaplug like this to go with it. First, turn the amp on manually. Then attach the plug to the end of the AC adapter's cord, plug the AC adapter into the accessory outlet on the 805, and plug the other end into the 7700's trigger connection. Once that is all done, the amp will turn on any time the 805 is on and turn off any time the 805 turns off.