JACK gets the "broken pipe" syndrome quite a lot, ie It never runs longer than like 5 minutes, and when it is (still) working, latencies need to be higher to avoid Xruns.
The AudioFire 2 used to playback a sterio using vlc player at 2millis, while with firmware 5.5 it needs around 5ms. An AudioFire 12 (12 channel), plays back on all 12 channels at 2 millis, which still has the 4.8 firmware on it,
and it's recorded 8+ tracks for 1hr 45 mins no Xrun no broken pipe.
That's my experience. This thread describes some peoples experience with ubuntu and an AudioFire 12,
and downgrading the firmware.