Let me add another vote for this feature.
I've been creating MP3 disks for my car stereo for a number of years. Like Eccles, I'd rather not have to adjust the volume control constantly. My solution has been to use the program
MP3 Gain. I've set track gain at 92db. I also have lossless versions on my PC of each track as well. It would be nice if MC could create the data disk and apply the replay gain so that the resulting disk would be volume leveled.
The same process could be used for output to folders on a hard drive or memory card. With many cell phones using microSD, I can see where MC users would want to sync to handheld AND have the files volume leveled at the same time. Have an option to "Apply Replay Gain on Output" and a way to set the volume level to a given level. Either a numeric value like 89 or 92, or +/- fixed amount, like we see in DSP studio.