Thanks Mark, I am that author
This can get a little confusing so I'll try to be concise...
Most modern DCC decoders can be run under DCC command (of course) or under DC current for traditional operation. To my knowledge they will not work on AC current. Contrary to popular belief DCC is not AC, but a pulse width modulated DC current.
Lionel Legacy and MTH ProtoSounds 3 electronics will run on AC current. If you want to add sounds to your AC powered engines I would contact Electric Railroad. They will have a product that will work for you.
Regards,