There have been several recent posts concerning adapting Aptosid for
music production, which did not sound to promising to me. If you want
a Debian-based Linux music distro, use AVLinux which runs tons of Linux
music apts out of the box, comes with a RT kernel (even 3.0 is
available), supports nearly any interface which can be supported in
Linux (e.g. firewire devices, using the "new stack").
IMHO is far easier to carve out a 20 GB partition and put AVLinux on it,
than to take a "generic" Linux distro and customize for music
production. You can still boot into your preferred distro/OS for other
tasks, though, you can still install any application you want from
Debian repos in AVLinux, so it works fine as a general purpose distro,
too.