Go to real OEM
You can get the PN for this and almost any other part on your car by checking out realoem.com, and following the prompts for your particular vehicle. It's a great resource I've used time and time again and is basically the same parts catalog your dealer uses.
My guess is that your p/n will be the same as for my non-DSP '99 540. Check it out and let me know what p/n realOEM gives you - I recently bought a used antenna amplifier for my car thinking I had a bad one. As it turns out my key fob is where my problem was, so I never installed the antenna amplifier I bought. I was going to hang on to it, but might be willing to let it go if it's the one you need.
Also - note that there are two "boxes" comprising the antenna amplifier - one in each C-pillar, next to the rear glass. So if RealOEM doesn't give you what you need, you can pry up the rear courtesy lights and lift off the c-pillar interior trim. It's only held on by a few clips and if you're careful you can re-use them. Once those trim pieces are off, you can easily see the amplifier boxes and their part numbers should be clearly labeled right on them.
PS - I believe this part was also used in the 7-series, but don't know which years.
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2006 Honda Odyssey EXL-RES
2006 Honda Accord V6 EX-L Sedan
1999 BMW 540i 6-Speed (Sold to M3UOND on 9/21/06)
1991 Honda Civic Si - Occasional Beater