Quoted from ForceFlow:Yes, L-2 should be the latest sound version for the L-4 game ROM.
Additionally, I had forgotten about the home ROMs. H-5 and H-6 is available. I'm not sure what the changes are, although H-6 is the profanity mod.
https://www.ipdb.org/machine.cgi?id=662
You may need to update the sound ROMs with the home ROMs.
I did the profanity sounds roms and yes you need to update the game rom to use them...there is also Soren's version that's available somewhere as well (nothing to do with the profanity version)