Were would that go? The author doesn't seem too keen on actually soldering on the inside of the devices, and they all give analogue out. Maybe you meant an amp?
A USB DAC connected to the old-laptop maybe? I have one on a Mini-PC that's the player for my music library - totally moved the digital-to-analogue conversion out of the noisy PC, and results in really clean audio. Obviously you get what you pay for - a £20 DAC wont do a very good job, but a £100 one will be good enough for most people.
