I work for a company on an Intel iMac running OS X 10.4.11 right now with FCP 6.0.4.
It’s very hard for me to work without waveforms when I’m editing, but it happens so frequently that all of a sudden my waveforms disappear and are replaced by those annoying x’s. I wish I had a definitive why, but here are a couple suggestions of things to try:
We work on multiple hard drives, so I’m constantly changing my scratch disks (and constantly forgetting to). I would check to see if your scratch disk does indeed point to where FCP has placed the waveform files.
Once you do that, if that doesn’t work I would recommend quitting FCP and cleaning up the old waveform files — especially if they’ve gone all over the place. (hey, it happens) When you open FCP, the hope is that it will realize the old ones are gone and make new ones.
Aside from that, sometimes it seems just quitting and reopening FCP itself will sometimes do the trick.
As far as slow waveform drawing, it doesn’t really matter the speed of your system, if you’re working off an external drive, it takes a while to run through the firewire (or USB if that’s your thing) to initially write the files — especially if you’ve got an hour or two worth of footage displayed in the timeline. Once they’re there though, they should be pretty quick to be displayed. One thing I tried, is what you can do is if you put all your capture scratch / render files on the external, you can keep the waveform and thumbnails on your internal HD, maybe in documents or whatever you like. That way they never have to be sent out via firewire.
Anyway, hope that helps some.