Most common wheels on 97 528?

Thanks to all the help out there I've nail down exactly what size tire is supposed to be on my 97 528 with 16 inch wheels. I appreciate it.
In 97 was the 16 inch rim some sort of factory upgrade from BMW? Most of
the 528's running around that appear to be that age seem to have a different wheel than mine. I'm pretty sure that what most of them have are 15 inch. Mine has 20 ribs and many that I see appear to have a crossed spoke look.
I've got the original sales papers that came with my car and nowhere on it is listed the wheel size, either standard or upgrade. It did have the "Premium Package" but not the "Sport Suspension ( if it was even offered then). The door jambs and the owners manual does list both the 15 inch and the 16 inch wheels. What came with 15 inch and what came with 16?
Final Question - The stereo seem pretty good. The sticker says 10 channel high performance system with 6 disk CD changer. There does not seem to have been an extra charge for it unless it was part of the "Premium Package". Is this stereo a good one and who is it made by? Can you find extra 6 disk cartridges for it?

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