The jailbreak has FM support for SMS and I believe it is enabled by default.
You either have to switch the core first (selecting SMS/SG-1000 from the core menu) to see the option in the Audio menu or launch the game and go back in the menu to toggle it. Can't recall off hand and not by my system.
Got it
MattWhite924 JamboGT
Cores -> SMS/SG-1000
Directory will display to select rom
Hit START for menu with new option
Core Options -> Use FM (YM2413) toggle
You can get back here pulling up the Sg menu (down+start by default) and hitting start to pull the menu back up
Can't flip it while the game is running so if you change after starting a game have to reset it
If you have Double Dragon can use this to compare. Non-FM version at the end of the video but it is extremely obvious when I turn it off it is easy to compare.