Hmm. I don't know much about AC's sound configuration in the files, but I think something in your common.bank is broken, or something akin to that. Like the car's not being read or something.
I would back up all my stuff like mods and profiles and do a good hard re-install. If that doesn't do it, then **** me. I was just driving the NSXs today, so I don't think it's on our end.
Okay, done that and still no cigar, never mind, obviously something wrong at my end as it seems to run well for others. Thanks for trying.