You mistakenly wrote "have no non-free drivers". Correct it please.
According to this announcement from DistroWatch, Musix does really have a real-time kernel. The latest development version is 3.0 beta 2 and can be downloaded here.
Ubuntu Studio had in the past a real-time kernel but as of version 10.10 they moved back to the monolithic-one. You can find a good software selection that can be helpful for you on its Wikipedia page here.
