Two to four Game Boy Advance systems are needed with one to three link cables. The game will allow up to three other players to mix records with the player at once. The record mixing is performed in the Record Corner…
I believe the problem may be one of two possibilities:
1) You need other people to mix records with. If you try to enter the room without other people to mix with, the game will keep sending out a signal, searching for other players until you press B. This is the most likely problem.
2) Another possibility is that it only works with a GBA, not a DS, due to technical limitations. I don't know for sure if the console makes any difference, it's only a theory.