If all else fails, do an audio mixdown. You can also output a QT Ref movie, reimport it and play off of that.
I know that you and many others don’t want to hear this but….
IMHO, FireWire drives, especially daisy chained ones are a lot less reliable with FCP 4-4.5 than they were in the past. Avoid them if possible. If you must use them, don’t fill them up too much and keep them maintained as you work with them, not just when they show signs of problems. If you are using a PowerBook, by all means, get a separate card bus adapter to separate the drives and the deck.
If you want more stability, go with internal SATA drives. Faster drives make all the difference with modern versions of FCP.
Kevin Monahan
Author – Motion Graphics and Effects in Final Cut Pro
fcpworld.com