AFAIK Knoppix is still a mix. Mostly from Sarge, some from Sid and perhaps even some from Stable. I haven't really been following the 3.8.1 very much but I'd be surprised if it's not a mix anymore. That's also a reason to install Sarge if you need compatibility with it. Or you could set testing (if it already isn't) as default in /etc/apt/apt.conf and do a dist-upgrade which should up-/downgrade most stuff to Sarge. Some packages will still get held if you don't force them. And yes, this will probably bork it even worse but should be fixable. If needed to up-/downgrade a held package try: apt-get -b --ignore-hold install held_package_name