Stereo music breaks the "3D effect" of music bricks wherein the closer you get to the brick, the louder the music is. Now, what you COULD do is separate the left channel from the right and make them two distinct .OGG files, then make a "stereo" in-game with two music bricks close to each other and use events so the channels sync up.
As for songs >1 MB, not gonna happen. I think a lot of people (including me) don't remember what music bricks were actually originally FOR: generic loops which add ambience to an environment.