[LAU] Fluidsynth, soundfonts, jack, and latency

Hello everyone, So I've been trying out AVLinux. By the looks of it, quite impressive - but I soon ran into a rather serious issue, but I doubt whether it has anything to do with AVLinux or not. I need your help in this knowing for sure. My usual setup involves a piano sample on Linuxsampler and a strings soundfont on qsynth. I had an unusual gig last week that required no piano sounds, but instead use of multiple layered samples. I therefore used only qsynth, with 3 engines running concurrently. So in my brand new AVLinux setup, I loaded up my samples, and had sooperlooper running 2-3 loops concurrently, all on a core2-duo macbook. Initially, all was ok. No noticeable latency, no xruns whatsoever.But during the rehearsals, this happened: after sometime, specially at some point when sooperlooper was running full steam, suddenly there was this HUGE latency, coupled with lots of dropped notes. As in, I could hold down a dozen keys simultaneously on the midi controller, and not all notes could be heard; those that did, would be heard at various instants upto about half a second later. Completely unuseable. This would persist even after restarting the jack server, but dissappear on rebooting the OS. To me, what is scary and irksome, is not (only) that this glitch happened consistently, but that there were no error messages in the qjackctl window. No xruns. Nothing that suggested that something had gone terribly wrong somewhere (which it had). I actually compromised on my gig sound, by offloading a lot of samples what I wanted layered. I don't know if it was because of this, but I didn't notice this particular issue on the gig itself (but it gave me sleepless nights prior). But then, 5 mins before the start of the program, I was left with no audio out of my system! (again, no error messages). Restarted jack server, and everything back to normal. Again, no error messages/warnings. Not so much as a by-your-leave. ;) I'm now intent on finding the source of the problem. I'm looking for pointers... where do I begin? Where's the 'smoking gun'? Thanks in advance! Cheers, Guru