I got the FTsim sounds working for all the variants following G550flyer's instructions above. Try copying these and see if they work for you. It looks like you have something different in the size and date lines.
{
"path": "SimObjects/Airplanes/MaddogX88/sound/MD80_Sp.PC.pck",
"size": 140886287,
"date": 133027422380000000
},
{
"path": "SimObjects/Airplanes/MaddogX83/sound/MD80_Sp.PC.pck",
"size": 140886287,
"date": 133027422380000000
},
{
"path": "SimObjects/Airplanes/MaddogX/sound/MD80_Sp.PC.pck",
"size": 140886287,
"date": 133027422380000000
},