When you shut off the receiver/amp, the power supply capacitors are still charged and it takes some time to deplete this charge.
To prevent electrical shock, you should wait some time, to be on the save side. Depending on the circuitry the large power supply capacitors are connected to, this may take some time. To be safe you could / should measure the remaining charge / voltage with a multimeter before you start working inside.
HiEnd fuses ? Sounds like a rip off to me.
If an amp blows its fuses, which are supposed to handle the load the amp was designed for, then something else must be wrong.
Never ever replace it with a stronger fuse or it might damage your amp or burn up your house as a worst case.
Look for the original source of the problem.