The AC12 can indeed be used both ways round, I understand.
I wanted to comment on this statement because someone was asking about using my extra adapters I made and later I realized they were going from SPDIF Preamp to SpeakerLink Speakers.
You should not use an AC12 in reverse (SPDIF to SpeakerLink) in any application in my opinion.
I'm 99% sure AC12 has attenuation (for going from SpeakerLink to SPDIF), like the adapters I just made.
If you run an AC12 or my adapter in reverse you'll get 0.5V SPDIF in and about 0.17V Out (not good), when it should be 2.0V out.
If you run a transformer only it will be 0.6V out.