I don´t know if this has already been discussed before elsewhere on these forums, but there is a better method of transfering custom BBS files into Daigasso!
You can download the Daigasso! Band Brothers save editor here.
http://zigg.com/code/dbbsed/
It has a really simple interface to load custom songs into your game, and you can have up to 8 custom songs at a time.
You can download the custom song BBS files here: http://www.gameswelike.com/games/bbmusictrade/bbsmusic.htm as well as plenty of other websites (mostly japanese) that can be found with some simple google searching.

I was wondering if anyone know how to use the Midi to BBS converter found here: http://www.maid.gr.jp/jubai/diary/blosxom.cgi/bandbrothers/rom/a200505270100.htm to make my own custom songs easily, or if there is a better tool to do that.