The AAmp is an analoge amplifier add-on to some HiFiBerry boards. It plugs on to of your HiFiBerry DAC board and adds a 60W analogue amplifier to it. Using an 12-20V power supply, it will not only power the amplifier, but also the DAC and Raspberry Pi.
You can use it with the following HiFiBerry boards that come with the necessary analoge output connector:
This is not a HAT that can be used standalone with the Raspberry Pi! It does not directly connect to the Raspberry Pi but it requires an additional supported HiFiBerry DAC board.