Second KXStudio (Score 2)

KXStudio is really the best choice if you want to give it a go on Linux. You can run whatever DE you want, gnome, kde, etc. Rosegarden will run just fine, even with a GTK DE (Gnome/Unity). So will QT based apps for that matter, just not as tight integration. I cant speak to transcription software, but Ardour is pro-quality multitrack audio, with decent and improving Midi capabilities. If you do opt for a Mac, I would highly recommend Reaper - for a $70 piece of software, it is quite amazing as a multitrack audio and midi studio.