Thanks for the pointers, that got it to do just what I wanted!

Now I just need to sit back and wait for it to tag all 14K songs They're hosted on a linux file server, but with Gigabit ethernet to my PC, the network isn't the bottleneck.

I like the option in there to overwrite the first 0.03 seconds of audio with the new v2 tag, but I'm not in a hurry... I'll just let it run all weekend.