I want something that runs the latest version of MuSE and
has a rt-kernel that is stable.

Well, I 've been using AVLinux for 6 months and I love it: it's really solid, stable and modern. also, it's the only distro that runs MusE 1rc3 pre-installed by default (please correct me if I am wrong).

About the kernel, I am not so technical, but about the apps -  it runs only a few (chosen?) apps but they are the ones that are actively maintained and developed

It's important to READ the instructions prior to installing it, as it will not work like your normal distro in many ways.
http://www.bandshed.net/AVLinux.html

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Viktor Mastoridis
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Merry Christmas and a Happy New Year
Убав Божиќ и Среќна Нова Година
Καλά Χριστούγεννα και Ευτυχισμένο το Νέο Ετος