By the way, some people tell that Zyn-fusion is not working well (see messages on http://lists.sourceforge.net/mailman/listinfo/zynaddsubfx-user). I didn't test it myself but upgrading to Zyn-fusion does not seem to be a priority. Another solution (if possible): compile two versions of zynaddsubfx, the "old" interface and the new one (zyn-fusion).