Noise measurement before mod. A little difficult, because the SPL meter doesn't go low enough. By placing it really close to the amp I managed to measure about 62 dB.

We start by removing the top. A lot of screws has to be removed (marked with red circles).

The long, grey thing is the heatsink(s) which all the air flow is supposed to go through. Between the fan and the heat sink(s) is a spacer that makes sure that all the air from the fan is directed through the heat sink(s).

The fan and grille is removed by unscrewing the shown screws.

We need a hole for the cables to the external fan. A vacuum cleaner ensures that no metal particles enters the amp.

Checking that the cables fits in the hole. Only the red and black wire is necessary. The yellow one can be cut.

Instead of making a new spacer, replacing the old fan, we just use casing of the old fan...

...by removing this.

Here's the fan casing in place, creating an air canal from the outside to the heat sink(s).

Then we fasten the 80mm -> 92mm adapter. The original screws works fine for this.

Fan and grille is installed with the screws included in the adapter kit. As we all can see, the clearance to the table is more than enough (at least 1 mm).

Note! The air direction is reversed ao that the fan now blows that air out of the back.

Then it's just the matter of soldering the wires of the new fan with the cut wires of the original fan. A 220 ohm / 1W resistor brings the voltage down to a level that fits the new fan (12V). The proper value of this resistor will vary with the fan used.

Here the resistor is soldered to the wire.

Then the resistor is attached to the chassis. A better placement would probably be to the heatsink, fastened with termal glue.

Measuring the noise level after the mod, shows no visible reading on the SPL meter, so I guess something went right...

A bad quality video showing the sound level difference before and after the mod (the audio level autogain on the camera certainly screws up this comparison, but you get the idea...)