I'm working on setting up a dedicated music box at home, and am running into a strange issue with ZynAddSubFx, I picked very non aggressive settings while trying to eliminate the jitter problems . First here is my setup:

Ubuntu 8.10
2.6.29.rc6-rt3 kernel
jack
256 Fraames/Period
Sample Rate 96000
Periods/Buffer 4
Realtime
Midi Driver: seq
resulting latency 10.7 ms
Maudio Omni i/o with Delta 44 sound card (ice1712 driver)
Maudio Axiom 61 midi keyboard

When I use qsynth with a soundfont loaded in it, there are no xruns, and no audio jitter.

When I use zynaddsubfx there are NO xruns, but there is audio jitter. I thought I saw news on the list of a new release of zynaddsubfx, but the last update on their sourceforge site was in 2005. Anyone on the list ever see this behavior from zynadsubfx.