My usual method for games that use a discrete sound CPU (like in this case) is to figure out how the main CPU communicates with the sound CPU.
Open the MAME source code and look for "sound latch" or similar, often you'll get the memory address. In this case, it's
here.
Then run MAME with the debugger enabled (mame64 -d cobracom), halt the main CPU early (usually by crashing it as soon as it starts), and you'll be able to send commands to the sound CPU without any interference.
I got music to play by entering this:
Code:
pc=8124
g
b@3e00=1f
This might sound complicated but it really isn't.