Your amplifier should have constant fused 12v power, a ground, and a switch wire. The switch wire should come from the radio head unit itself, and will tell the amp to turn on when power to the radio is on. You probably shouldn't be connecting stereo amplifiers up to a multi-use fuse block with other accessories drawing power from the same feed wire. You want amplifiers to get all the power they need to run efficiently.
Here is a link with an amplifier setup.
http://www.crutchfield.com/S-4…r_installation_guide.html
This one should answer the other quesstions you might have about powering amplifiers.
http://www.crutchfield.com/S-u…r/car/amplifiers_faq.html
Use the fuse block to power other small acessories like lights and 12v outlets, and such.
Stephen