I assume you are new to electronics. See if you can find anything about discharging the power supply caps. A lot of amps will hold dangerous levels of voltage in their power supplies. Learn how to drain these (caps) first. Shutting an amp off while music is playing may drain some voltage, but even if it does, you need to discharge the rest of its voltage first.
schematically speaking
I have been toying with the idea of tweeking a cheap amp. Caps power supply etc. After getting a feel for it I thought I might move onto something of value. Are schematics readly available for amps such as adcom, sony, onkyo etc? Also I presume that I can replace a cap with a like cap of a different manufacturer?