I had a nice chat with Dan at Bel/Escort about if and when the new firmware for the STi which incorporates the latest audio ramp-up fix was introduced. It took a while for him to check with engineering, but he came back and told me that the new firmware was introduced on the production line starting with week 42 of 2008. Thus all STi's produced during and after 4208 have the new firmware which includes the new audio ramp-up!
I should have checked into this at least a few months ago in order to find out if and when the new firmware was introduced onto the STi production line. My apologies.