I found this:

http://www.bit-tech.net/article/70/

Does something similar to what you want - I imagine if you wired this up, but instead wired the amp remote line up to the normally-closed relay outputs - it would switch from normally-closed to normally-open on powerup, and then after the delay, switch back to normally-closed, providing power.

Don't know if this helps, or even works.

Cheers,

A.