I don't think there's a dedicated tool for that
I use Usagi to hear the music (go to 3dsthem.es, download any theme, extract the body_LZ.bin, rename the bcstm you want to bgm.bcstm, download and run Usagi, then load the body_LZ.bin. then you should be able to play it)
(go to 3dsthem.es, download any theme, extract the body_LZ.bin, rename the bcstm you want to bgm.bcstm, download and run Usagi, then load the body_LZ.bin. then you should be able to play it)