it seems to me that since mp3 and ogg vorbis have different tagging systems that there might be discrepancies.

Ah. The key piece of information you're missing is:

The Cambridge team has always designed their products to work off of their own internal database. Never directly off of the tags.

When you put an MP3 file into any of their products (be it the empeg car, the Karma, the Rio Central, whatever), it only touches the tag the very first time it's dropped into the software (emplode, Rio Music Manager, whatever). It reads the tag just that once, to import the track information into its database.

From that moment on, the player has no concept of tags. The player software itself can't even read the tags. Only Emplode/RMM can read the tags, and only at the initial import time. Everything else except that initial import is done in the database.

The database entry for each song file is the same. The only thing that differs in the database between an Ogg file and an MP3 file is the one flag telling it which audio stream decoder to use when playing it. Everything else that deals with the song file is identical regardless of the file format.

So that's why your question seemed so strange to us. We knew that key tidbit of information (and now you do, too. ).