I have a 2004 BMW that has an original 80G phatbox in it with Blitzsafe connector. Unfortunately, the box gave up the ghost and is no longer working.
Are you sure it is the Phatbox? The circuit board in the Blitzsafe has an annoying tendancy to shift, which causes a poor connection to the DIN cable coming from the Phatbox. Somewhat less likely are the 3- and 6-pin cables that connect to the car coming loose.
First, when the Audi one arrives, can I just pull out the innards and put them in the BMW case so install in the car remains simple? I think that is a simple swap and only the cases differ, but can someone confirm?
There are a number of different revisions of the Phatbox, but the two case styles are interchangeable. You should be able to swap with no problem.
Second, since the new box was loaded with Audi software, I guess I have to purge that and install BMW software. Since the original software is no longer supported, should I uninstall all my MM software on my computer and reinstall with PhatHack? Then re-program my Phatbox?
You'll need to flash the Phatbox with the BMW firmware. The firmware that talks to the particular type of head unit (BMW / Audi / Kenwood / etc.) is stored in flash memory on a secondary microprocessor in the Phatbox.
I'm not sure if the original Music/Media Manager can find the online updates (they were on the old Phatnoise server, and I'm not sure if they are re-hosted in a place where PMM can find them). PhatHack can certainly do it. Since this will be an original DMS, don't check the "install hacked firmware" option. Once you have the new box up and running, you'll probably want to hack it so you can use a different hard drive in the future.