[LAU] Jack frequently crashes when running LinuxSampler + Qsynth

Hello everyone, This is my first post on this list. My compliments & gratitude to everyone working towards Linux Audio! I'm a semi-pro musician (keyboardist + singer), and for the past few months have been working on a linux-based setup for live performances. Here's what I use: 1. LinuxSampler, which loads my main piano sample. I depend on this sample throughout the performance (it happens to be a 888 MB sample). I also have additional pianos and drums loaded on. The other pianos are more of a backup, but I almost never use them. Drums are triggered by a Korg NanoPad. 2. Qsynth, on which I have a few string soundfonts on different channels, totalling less than 20 MB. Typically these are layered on top of tmy main piano sample. 3. I use a python script based on Mididings to for midi processing, to achieve splits and layers, and map hardware controllers. 4. JackMixDesk as a software mixer, to adjust the levels of the various layers, and vocals. 5. Jack-Rack, loading Calf reverb plugins + amplifier, for vocals. 6. Everything started through QJackCtl. I use a Casio keyboard as a Midi controller (thru USB) and a Korg NanoKontrol. I recently migrated from a Celeron laptop to a core2 duo Macbook, both running Ubuntu 9.04. On both, I've been using the builtin soundcards. After migrations, there's been a persistant issue with Jack's stability: -After a few minutes of playing on the keyboard, the sound from the samples become horribly distorted, crackly, buzzy and tinny (sorry, thats the best description I can give!). -At the instant of this 'crash', this appears in the Messages window of qjackctl: "subgraph starting at LinuxSampler1 timed out (subgraph_wait_fd=31, status = 0, state = Finsihed, pollret = 0 revents = 0x0) -When I restart Qsynth, it says "Qsynth1: Failed to create te audio driver (jack). Cannot continue without it". Upon restarting Jack, everything's happily back to normal, until the crash happens again. I checked with the system monitor, and the resource usage is well within limits - max of ~80% CPU/core, and less than 50% of RAM being used at any point of time. Needless to say, this effectively rules out using my linux system as a live performance tool. Like all stage musicians, I place a VERY high premium on stability. But I would love to have a completely open-source setup - so any pointers/help would be greatly appreciated! Cheers, Guru