All the data you're looking for in contained in the directory area of the storage device (SD, hard drive, whatever) for that MP3 file (like any digital file, i.e., name - but with the additional metadata of the group name, genre, even a picture, etc.)
Like I said, you'll have to extract the genre data from within all of the above. Only way to do that is with a ucontroller (device in your flow chart) that has the code to "read" only that portion of the directory entry, compare it against your "genre" database and then enable the correct switching needed to output the music file to the correct amplifier.
Since you're planning on using a PC or i(thing) for your playback "device", you're going to have to hack that device somehow to extract the metadata you want. That is another beast altogether since you're going to have to use the OS for that device. Doable, I suppose, as an app for that machine.
Maybe misterT has some ideas...?