I am running an iMac rev B/96 megs ram/9.0. I used to use my burner under 8.6 though. Toast 4.0 and the Sony Spressa are a buggy combination at best. However, it still blows away Discribe. I just burned 4 cds last night with Toast, though, only to find that my computer wouldn't recongize the drive today. This was frustrating. I ended up having to turn on toast, turn off my burner, then turn the Spressa back on again. After doing this, Toast would recognize the drive again. You may need to try and fiddle around the Spressa like that.
As for my extensions:
Toast USB Shuttle Bridge
Toast USB ShuttleIn Bridge
Toast USB Support
I'm not sure if you need anything else installed. I'd be willing to try and help, but let me know what extensions and such you are already using. Mind you, even if you get Toast to recognize the drive, you will still have problems when burning some disks. I can explain a few if you'd like. Just let me know.
-S