Flash the US device with the European ROM (which involved tricking the ROM installation program by switching ROM files after it did its check and before it did the install) and just like that the US device could play Vorbis. How MS bullied or bribed the manufacturer to omit Vorbis from the US ROM I don't know.
The bullying was done as part of the PlaysForSure program.
That was microsoft's attempt to counter music stores like iTunes and co. They had a platform for selling DRM-ed music in WMA format. OEMs had to undergo a certification to be able to advertise "Microsoft PlaysForSure". That mandated certain formats (support for DRM, support for WMA). It was worded in such a way that it basically forbid manufacturer to put any other codec on the device (see the "Criticisms" section. According to MS that was due to a junior employee who wrote it. Yeah. Sure.). It think the controversy was talked about back then here on /.
My opinion is that this probably started as an attempt to initially close loop-hole to avoid consumer playing non DRM-ed / unlicensed music (i.e.: pirated), but at the hand of MS executive quickly evolved as a way to attempt crushing competition.
That severly limited the spreading of non-WMA formats (free like Vorbis or FLAC. Or alternative licenses like Sony's ATRAC, etc.) because OEMs probably feared that including extra formats would exclude them from WMA certification and they would lose market share to manufacturer who didn't.
(Specially since back then, Vorbis didn't have any markets, it was mostly used for higher quality home rips. Whereas WMA had Microsoft's store and OEMs were hoping to have something against the iTunes behemoth).
Or mostly so in the US.
The rest of the world didn't give a damn fuck about microsoft's market (was is even available outside US ?) nor play for sure. People wanted mainly MP3 because that was the most widespread format, and adding extra formats was a way for OEM to put more tick box on their feature list. As such adding Vorbis was a win-win: it doesn't cost anything (and even had a BSD licensed integer implementation for embed available for free) and was one extra feature that they'll advertise to gain attraction. Every single asian no-name manufacturer did add it.
In Europe nearly every player I've seen in store did have Vorbis support.
That explains the dual ROM:
- one ROM to placate microsoft to get access to PlaysForSure in the US market.
- one ROM with as many features as possible cramed in to gain visibility everywhere else.