I used Ardour, Sfizz for SFZ and Virtual Playing Orchestra (VPO) to compose some classical (film) music.
Check out the middle part of Jäger.
I think it is amazing what you can do with those three packages.
Maybe the following is helpful for future composers googling around:
- I had to fix a bug with Sfizz playback but other than that it worked flawlessly.
- I compressed VPO with FLAC to 668MB since Sfizz is able to read FLAC.
- I installed Deb packages from Debian experimental on Ubuntu. Sometimes I had to (dpkg -i --force-depends) but it works as expected.