Kxstudio has added Zyn-Fusion to their repo’s, what joy!
I highly recommend you try this new gui to Zynaddsubfx, it really is nice!
This latest version of Zynadd’ works as a stand alone synth or as a plugin. It integrates beautifully with Ardour!
If you haven’t installed it already, just ‘apt-get install zynaddsubfx-git’ (assuming you have the Kxstudio repo’s enabled (see my build page).