URC's database on Sony codes (especially the old codes) is pretty complete. I would be beyond amazed if the Harmony database (which is very good) had some old Sony codes that URC didn't.

With the 707ES turned on; pull power to it, wait a minute and plug it back in. See if it comes back on or if it powers up in an off state. If it comes back on when plugged in, try unplugging it for an hour to make sure it comes back on when plugged in (if it was on when unplugged). If it does, you can use a switched outlet to turn it off & on.

I have used these with success in the past. Plug your amp into the Control outlet and when you turn your amp off & on, it will switch the other outlets off & on. (Amp has to draw at least 7+ watts when on, to trigger the switch).
[Link: amazon.com]