I removed and reinstalled the drivers which solved the analog output issue, which is good. Then I decided to actually test SPDIF passthrough; the release notes still say it's not supposed to work on x64, but that hasn't stopped me from trying with every
previous version, and it wouldn't stop me now.
And it works! As I type this, I have a DVD playing in PowerDVD7, and SPDIF passthrough works perfectly.
After two years (including the betas) of having to reboot into XP to watch DVDs, I can finally, finally do it in Vista.
I'm happy now.