The best place to start at learning mastering IMHO is loudspeaker building and design. The reverse engineering here will assist you in knowing why some loudspeakers sound the way they do and others sound different for the good and the not so good. Taking loudspeakers and acoustics into consideration you then have a feel for what translation is all about as most mastering engineers evaluate on several different systems. Once you can brain extrapolate what your project will sound like on other systems including wealkman headphones and high end stereo systems then you have a directional edge in the art. All that being said you really don't have to build 100 different pairs of speakers to gain this knowledge but knowing other speakers is only one key element. Wow...It is getting late for me...I will come back and revisit this thread and have more details....this is just the tip of the iceberg...it gets a whole lot deeper.