Like this scavenged TDA1558Q from that stereo. (On the heat sink)
I did something like this before by taking the set up out of a gaming chair with the speakers, inputs, and volume control, that was nice but it didn’t have the bass that I really wanted from a portable stereo. My improved version has the bass that I was looking for and has the volume control from the audio input device (i.e. Mp3, ipod, iphone, etc.).