Thanks for that Paul. That’s sort of what I found, that Fraunhofer put it out more than 10 years ago, but seemed to drop support and moved on to AAC.
It seems like the practical options for comparison of lossy 5.1 are probably:
Fraunhofer codec AAC 5.1 (in Wavelab)
Apple codec AAC 5.1 (on Mac, as ShikiSuen suggested above)
Apple codec AAC 5.1 (on Windows, with QAAC plugin in Foobar2000)
Dolby AC3 (in MediaHuman Audio Converter and others)
Maybe there are others.