you should stick to what is available in our package manager Synaptic because we have tested these programs for our distribution. Anythiong from outside may break your system and we can no longer help you then.
wrt FullMonty, please read this
page as well as the maintenance
page, especially point 7 in the first post, which will tell you to uninstall MIXXX and then install its newer version (or not if you don't want it) before upgrading the system.