http://iceteam.altervista.org/sidin.php

For totally reverse engineered work, look at:

#1 Ripping Dig Dug
#2 Inside Lazy Jones | Inside Driller
#4 Inside Arkanoid
#6 Inside DigiOrganizer
#7 Inside Modules
#14 Inside Hunter's Moon
#15 Inside Serpent Demo

Usually the I/o mapped chips help a lot in understanding the code.

For example, with sid music the D4xx range of read/write is the first point I look for.

This is else why the program automatically comments know memory location giving the meanings:

$D418 ; Sid volume and filter mode

I look for ...

Even if the answer comes near an year later, you should use JC64dis for this task (https://iceteam.itch.io/jc64dis).
Version 1.0 else will support cartridge loading directly.

I reverse enginnering many music players over the years for having a commented source code that can compile back to binary ...