Since you have the sys11 you most likely have the p-6 roms from the samples and early productions. These cannot be changed. Some experimenting was done in the FH owners club though and it was found that you CAN change the sound roms, but it really doesn't make a difference as you can't use the 1 different callout since the older ROM doesn't have it.
I too have a sys11 game and you really aren't missing anything. There is really only one big difference and that is an additional light show and the 'you big sausage' callout.
Does your playfield have S-T-E-P or S-T-E-P-S and do you have red or green boards?