Except Toast (20 Pro is the version I have) quietly only supports discs with stereo audio, not 5.1. And 5.1 discs are what I make.
A disc with a 5.1 soundtrack will appear to burn just fine but will play back sped up. No messaging, no warning, just a terrible user experience. And Roxio's support is dreadful.
The Toast option was meant to be the Apple-suggested workaround for blu ray when Final Cut dropped it but, in my case at least, I need a workaround for the workaround. Until then, or until I know for sure FCP 10.7.1. will work with Tahoe, I'll stay put. I'm not in that much of a rush that I need to faff around with external disc installs, but thanks for the suggestion.