The reason I prefer to go with Firewire is because I worry about the other USB devices (mouse, keyboard, midi keyboard, security dongle) interfering with the audio interface. I like that there's nothing else in the chain to muck things up.
In any case, I was able to purchase the FA-101 at a decent price ($150 less than MSRP) and almost all my problems are gone. The squealing sound due to CPU usage is history, and my multitrack playback is clean. But I still get crackling when using one plugin (video playback for writing music to picture). Again, no amount of changes to settings for buffering and latency make it go away.
I've also noted in the manual that TI is highly suggested, so I'll just switch out my firewire card and ...hopefully... that'll fix the crackling for that one plugin.