Well, heres an answer, but not a complete one...
Your description of tweaking the RG settings will certainly work in MC playback for volume levelling, but I cant say if it will work on files transferred to any particular player.
My understanding is that ReplayGain is simply a number stored in a tag. The number is used by MC to adjust the volume for that file. Unless your player knows how to use that tag, files transferred elsewhere wont be volume levelled using RG. Also, converting/transferring RG'ed files in MC will not actually apply the RG values to produce volume levelled files. Theres a piece of software (not from JRiver) called MP3Gain which will do this - the downside (?) being that it alters the entire mp3 music file data to reduce the volume, rather than just changing a tag.
Ludwig, it sounds from what youre saying that the Ipod/Ipod plugin somehow does take account of RG info in preparing files for transfer. I havent got one so I dont know - if youre not getting any joy Id suggest a repeat post to the Ipod thread, where Im sure Steve can give you the lowdown.
Hang in there - someone who really knows what they are talking about will surely post soon.