It wouldn't be much work to set up. I'm only thinking of about three or four distinct values across the entire volume range from min vol to 0dB. I'm not saying that this is a trivial task for the programmers though. Your method's OK but I think my method gives you more scope to get it just right. It would also cope better with the natural variation in gain at different frequencies of individual setups. Don't forget that the interior space of your vehicle acts as an amplifier (more so at the lower frequencies than at the higher) and this wil be different for each vehicle (although it probably marginal). I don't know whether this would put much extra stress on the processor though. Anyway I think it would be yet another cool feature to show off the player to your friends.