I've done 1000s of bm54 upgrades. A guy wanted auxiliary input on the Back unit and so I did the firmware upgrade, which worked, but no sat Nav voice. It would lower the volume of the music, but nothing comes out. I would also assume, that the tv sound would not work, as it shares the same input on the bm54 back.
I never tested the Back with regards to audiotext from an MP3 changer. No point I guess, as if you can't have sat Nav voice, then there is no point IMO.
Better off buying a flat pin bm54, more options and more use of the firmware upgrade, with dynamic routing, auxiliary iD3 tags, better radio control etc.
The amp upgrades are the first port of call on these units. No point of doing anything with a ticking time bomb on the IC amps, which fail and are the worst sound quality in any car I've ever been in.

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