I have an AudioSource AMP-100 audio amp, and I want to be able to turn it off and on remotely. I'm wondering how safe it is to just cut the power to the amp; it seems like this is what the power switch does already. I would use a relay or something similar to cut the power or restore it. The amp would be in standby (a state it goes into when there's no input signal) when it gets turned off.
Depending on your amp, the on off switch may do many things, not just cut power. I would suggest your best course of action may be to look carefully at the circuitry- if it does just cut power at the mains side of the power supply circuitry you should be safe.
If it cuts power on the amp side then you could risk large spikes sent to the speakers, which could cause damage.
If it does something more complex, like running chilling fans on a timer, discharging or charging capacitors etc then you could destroy your amp.
Update - when you look at the circuitry, also check to see whether the on-off switch is just a single switch, or whether it switches multiple circuits (which is very common). If it is a single switch, you probably could replace it with a remote controlled relay, as per @FriendofGeorge's comment.
Really depends on the amp. If the amp is designed to cool itself after turning off, then it could be bad to simply cut the power, but if it doesn't have cooling needs, then cutting power should be fine.